{"id":85234,"date":"2022-02-08T15:30:34","date_gmt":"2022-02-08T10:00:34","guid":{"rendered":"https:\/\/www.cbselabs.com\/?p=85234"},"modified":"2022-02-08T15:45:47","modified_gmt":"2022-02-08T10:15:47","slug":"important-questions-for-class-10-maths-chapter-6","status":"publish","type":"post","link":"https:\/\/www.cbselabs.com\/important-questions-for-class-10-maths-chapter-6\/","title":{"rendered":"Important Questions for Class 10 Maths Chapter 6 Triangles"},"content":{"rendered":"
Triangle Questions Class 10 Question 1.<\/strong> Class 10 Triangles Important Questions With Solutions Pdf Question 2.<\/strong> Triangles Class 10 Important Questions Question 3.<\/strong> Triangles Important Questions Class 10 Question 4.<\/strong> Triangles Class 10 Important Questions With Solutions Question 5.<\/strong> Triangle Important Question Class 10 Question 6.<\/strong> Triangles Questions Class 10 Question 7.<\/strong> Questions On Triangles Class 10 Question 8.<\/strong> Triangles Class 10 Questions Question 9.<\/strong> Class 10 Maths Chapter 6 Extra Questions Question 10.<\/strong> Question 11. Question 12. Question 13. Question 14. Question 15. Question 16. Question 17. Question 18. Question 19. Question 20. Question 21. Question 22. Question 23. Question 24. (b) In \u2206ABE and \u2206DBC, Question 25. Question 26. Question 27. Question 28. Question 29. Question 30. Question 31. (ii) \u2234 \\(\\frac{A B}{A D}=\\frac{B C}{D E}=\\frac{A C}{A E}\\) … [side are proportional Question 32. Question 33. Question 34. Question 35. Question 36. Question 37. Question 38. Question 39. Question 40. Question 41. Question 42. Question 43. Question 44. Question 45.
\nIf \u2206ABC ~ \u2206PQR, perimeter of \u2206ABC = 32 cm, perimeter of \u2206PQR = 48 cm and PR = 6 cm, then find the length of AC. (2012)
\nSolution:
\n\u2206ABC ~ \u2206PQR …[Given
\n<\/p>\n
\n\u2206ABC ~ \u2206DEF. If AB = 4 cm, BC = 3.5 cm, CA = 2.5 cm and DF = 7.5 cm, find the perimeter of \u2206DEF. (2012, 2017D)
\nSolution:
\n\u2206ABC – \u2206DEF …[Given
\n
\n<\/p>\n
\nIf \u2206ABC ~ \u2206RPQ, AB = 3 cm, BC = 5 cm, AC = 6 cm, RP = 6 cm and PQ = 10, then find QR. (2014)
\nSolution:
\n\u2206ABC ~ \u2206RPQ …[Given
\n
\n\u2234 QR = 12 cm<\/p>\n
\nIn \u2206DEW, AB || EW. If AD = 4 cm, DE = 12 cm and DW = 24 cm, then find the value of DB. (2015)
\nSolution:
\nLet BD = x cm
\nthen BW = (24 \u2013 x) cm, AE = 12 – 4 = 8 cm
\nIn \u2206DEW, AB || EW
\n<\/p>\n
\nIn \u2206ABC, DE || BC, find the value of x. (2015)
\n
\nSolution:
\nIn \u2206ABC, DE || BC …[Given
\n
\nx(x + 5) = (x + 3)(x + 1)
\nx2<\/sup> + 5x = x2<\/sup> + 3x + x + 3
\nx2<\/sup> + 5x – x2<\/sup> – 3x – x = 3
\n\u2234 x = 3 cm<\/p>\n
\nIn the given figure, if DE || BC, AE = 8 cm, EC = 2 cm and BC = 6 cm, then find DE. (2014)
\n
\nSolution:
\nIn \u2206ADE and \u2206ABC,
\n\u2220DAE = \u2220BAC …Common
\n\u2220ADE – \u2220ABC … [Corresponding angles
\n\u2206ADE – \u2206\u0391\u0392C …[AA corollary
\n<\/p>\n
\nIn the given figure, XY || QR, \\(\\frac{P Q}{X Q}=\\frac{7}{3}\\) and PR = 6.3 cm, find YR. (2017OD)
\n
\nSolution:
\nLet YR = x
\n\\(\\frac{\\mathrm{PQ}}{\\mathrm{XQ}}=\\frac{\\mathrm{PR}}{\\mathrm{YR}}\\) … [Thales’ theorem
\n<\/p>\n
\nThe lengths of the diagonals of a rhombus are 24 cm and 32 cm. Calculate the length of the altitude of the rhombus. (2013)
\nSolution:
\nDiagonals of a rhombus are \u22a5 bisectors of each other.
\n\u2234 AC \u22a5 BD,
\nOA = OC = \\(\\frac{A C}{2} \\Rightarrow \\frac{24}{2}\\) = 12 cm
\nOB = OD = \\(\\frac{B D}{2} \\Rightarrow \\frac{32}{2}\\) = 16 cm
\nIn rt. \u2206BOC,
\n<\/p>\n
\nIf PQR is an equilateral triangle and PX \u22a5 QR, find the value of PX2<\/sup>. (2013)
\nSolution:
\nAltitude of an equilateral \u2206,
\n<\/p>\nTriangles Class 10 Important Questions Short Answer-I (2 Marks)<\/h3>\n
\nThe sides AB and AC and the perimeter P, of \u2206ABC are respectively three times the corresponding sides DE and DF and the perimeter P, of \u2206DEF. Are the two triangles similar? If yes, find \\(\\frac { ar\\left( \\triangle ABC \\right) }{ ar\\left( \\triangle DEF \\right) } \\) (2012)
\nSolution:
\nGiven: AB = 3DE and AC = 3DF
\n
\n…[\u2235 The ratio of the areas of two similar \u2206s is equal to the ratio of the squares of their corresponding sides<\/p>\n
\nIn the figure, EF || AC, BC = 10 cm, AB = 13 cm and EC = 2 cm, find AF. (2014)
\n
\nSolution:
\nBE = BC – EC = 10 – 2 = 8 cm
\nLet AF = x cm, then BF = (13 – x) cm
\nIn \u2206ABC, EF || AC … [Given
\n<\/p>\n
\nX and Y are points on the sides AB and AC respectively of a triangle ABC such that \\(\\frac{\\mathbf{A X}}{\\mathbf{A B}}=\\frac{1}{4}\\), AY = 2 cm and YC = 6 cm. Find whether XY || BC or not. (2015)
\nSolution:
\nGiven: \\(\\frac{A X}{A B}=\\frac{1}{4}\\)
\n
\nAX = 1K, AB = 4K
\n\u2234 BX = AB \u2013 AX
\n= 4K – 1K = 3K
\n
\n\u2234 XY || BC … [By converse of Thales’ theorem<\/p>\n
\nIn the given figure, \u2220A = 90\u00b0, AD \u22a5 BC. If BD = 2 cm and CD = 8 cm, find AD. (2012; 2017D)
\n
\nSolution:
\n\u2206ADB ~ \u2206CDA …[If a perpendicular is drawn from the vertex of the right angle of a rt. \u2206 to the hypotenuse then As on both sides of the \u22a5 are similar to the whole D and to each other
\n\u2234 \\(\\frac{B D}{A D}=\\frac{A D}{C D}\\) …[\u2235 Sides are proportional
\nAD2<\/sup> = BD , DC
\nAD2<\/sup> = (2) (8) = 16 \u21d2 AD = 4 cm<\/p>\n
\nIn \u2206ABC, \u2220BAC = 90\u00b0 and AD \u22a5 BC. Prove that AD\\frac{B D}{A D}=\\frac{A D}{C D} = BD \u00d7 DC. (2013)
\nSolution:
\nIn 1t. \u2206BDA, \u22201 + \u22205 = 90\u00b0
\nIn rt. \u2206BAC, \u22201 + \u22204 = 90\u00b0 …(ii)
\n\u22201 + \u22205 = \u22201 + \u22204 …[From (i) & (ii)
\n.. \u22205 = \u22204 …(iii)
\nIn \u2206BDA and \u2206ADC,
\n
\n\u22205 = 24 … [From (iii)
\n\u22202 = \u22203 …[Each 90\u00b0
\n\u2234 \u2206BDA ~ \u2206ADC…[AA similarity
\n\\(\\frac{B D}{A D}=\\frac{A D}{C D}\\)
\n… [In ~ As corresponding BA sides are proportional
\n\u2234 AD2<\/sup> = BD \u00d7 DC<\/p>\n
\nA 6.5 m long ladder is placed against a wall such that its foot is at a distance of 2.5 m from the wall. Find the height of the wall where the top of the ladder touches it. (2015)
\nSolution:
\nLet AC be the ladder and AB be the wall.
\n
\n\u2234Required height, AB = 6 m<\/p>\n
\nIn the figure ABC and DBC are two right triangles. Prove that AP \u00d7 PC = BP \u00d7 PD. (2013)
\n
\nSolution:
\n
\nIn \u2206APB and \u2206DPC,
\n\u22201 = \u22204 … [Each = 90\u00b0
\n\u22202 = \u22203 …[Vertically opp. \u2220s
\n\u2234 \u2206APB ~ \u2206DPC …[AA corollary
\n\u21d2 \\(\\frac{\\mathrm{BP}}{\\mathrm{PC}}=\\frac{\\mathrm{AP}}{\\mathrm{PD}}\\) … [Sides are proportional
\n\u2234 AP \u00d7 PC = BP \u00d7 PD<\/p>\n
\nIn the given figure, QA \u22a5 AB and PB \u22a5 AB. If AO = 20 cm, BO = 12 cm, PB = 18 cm, find AQuestion (2017OD)
\n
\nSolution:
\n
\nIn \u2206OAQ and \u2206OBP,
\n\u2220OAQ = \u2220OBP … [Each 90\u00b0
\n\u2220AOQ = \u2220BOP … [vertically opposite angles
\n<\/p>\nTriangles Class 10 Important Questions Short Answer-II (3 Marks)<\/h3>\n
\nIn the given figure, CD || LA and DE || AC. Find the length of CL if BE = 4 cm and EC = 2 cm. (2012)
\n
\nSolution:
\nIn \u2206ABL, CD || LA
\n<\/p>\n
\nIf a line segment intersects sides AB and AC of a \u2206ABC at D and E respectively and is parallel to BC, prove that \\(\\frac{A D}{A B}=\\frac{A E}{A C}\\). (2013)
\nSolution:
\nGiven. In \u2206ABC, DE || BC
\n
\nTo prove. \\(\\frac{\\mathrm{AD}}{\\mathrm{AB}}=\\frac{\\mathrm{AE}}{\\mathrm{AC}}\\)
\nProof.
\nIn \u2206ADE and \u2206ABC
\n\u22201 = \u22201 … Common
\n\u22202 = \u22203 … [Corresponding angles
\n\u2206ADE ~ \u2206ABC …[AA similarity
\n\u2234 \\(\\frac{\\mathbf{A D}}{\\mathbf{A B}}=\\frac{\\mathbf{A} \\mathbf{E}}{\\mathbf{A C}}\\)
\n…[In ~\u2206s corresponding sides are proportional<\/p>\n
\nIn a \u2206ABC, DE || BC with D on AB and E on AC. If \\(\\frac{A D}{D B}=\\frac{3}{4}\\) , find \\(\\frac{\\mathbf{B} C}{\\mathbf{D} \\mathbf{E}}\\). (2013)
\nSolution:
\nGiven: In a \u2206ABC, DE || BC with D on AB and E
\non AC and \\(\\frac{A D}{D B}=\\frac{3}{4}\\)
\nTo find: \\(\\frac{\\mathrm{BC}}{\\mathrm{DE}}\\)
\nProof. Let AD = 3k,
\n
\nDB = 4k
\n\u2234 AB = 3k + 4k = 7k
\nIn \u2206ADE and \u2206ABC,
\n\u22201 = \u22201 …[Common
\n\u22202 = \u22203 … [Corresponding angles
\n\u2234 \u2206ADE ~ \u2206ABC …[AA similarity
\n<\/p>\n
\nIn the figure, if DE || OB and EF || BC, then prove that DF || OC. (2014)
\n
\nSolution:
\nGiven. In \u2206ABC, DE || OB and EF || BC
\nTo prove. DF || OC
\nProof. In \u2206AOB, DE || OB … [Given
\n<\/p>\n
\nIf the perimeters of two similar triangles ABC and DEF are 50 cm and 70 cm respectively and one side of \u2206ABC = 20 cm, then find the corresponding side of \u2206DEF. (2014)
\nSolution:
\n
\nGiven. \u2206ABC ~ \u2206DEF,
\nPerimeter(\u2206ABC) = 50 cm
\nPerimeter(\u2206DEF) = 70 cm
\nOne side of \u2206ABC = 20 cm
\nTo Find. Corresponding side of \u2206DEF (i.e.,) DE. \u2206ABC ~ \u2206DEF …[Given
\n
\n\u2234 The corresponding side of ADEF = 28 cm<\/p>\n
\nA vertical pole of length 8 m casts a shadow 6 cm long on the ground and at the same time a tower casts a shadow 30 m long. Find the height of tower. (2014)
\nSolution:
\n
\nLet BC be the pole and EF be the tower Shadow AB = 6 m and DE = 30 m.
\nIn \u2206ABC and \u2206DEF,
\n\u22202 = \u22204 … [Each 90\u00b0
\n\u22201 = \u22203 … [Sun’s angle of elevation at the same time
\n\u2206ABC ~ \u2206DEF …[AA similarity
\n\\(\\frac{A B}{D E}=\\frac{B C}{E F}\\) … [In -As corresponding sides are proportional
\n\u21d2 \\(\\frac{6}{30}=\\frac{8}{\\mathrm{EF}}\\) \u2234 EF = 40 m<\/p>\n
\nIn given figure, EB \u22a5 AC, BG \u22a5 AE and CF \u22a5 AE (2015)
\nProve that:
\n(a) \u2206ABG ~ \u2206DCB
\n(b) \\(\\frac{\\mathbf{B C}}{\\mathbf{B D}}=\\frac{\\mathbf{B E}}{\\mathbf{B A}}\\)
\n
\nSolution:
\n
\nGiven: EB \u22a5 AC, BG \u22a5 AE and CF \u22a5 AE.
\nTo prove: (a) \u2206ABG – \u2206DCB,
\n(b) \\(\\frac{B C}{B D}=\\frac{B E}{B A}\\)
\nProof: (a) In \u2206ABG and \u2206DCB,
\n\u22202 = \u22205 … [each 90\u00b0
\n\u22206 = \u22204 … [corresponding angles
\n\u2234 \u2206ABG ~ \u2206DCB … [By AA similarity
\n(Hence Proved)
\n\u2234 \u22201 = \u22203 …(CPCT … [In ~\u2206s, corresponding angles are equal<\/p>\n
\n\u22201 = \u22203 …(proved above
\n\u2220ABE = \u22205 … [each is 90\u00b0, EB \u22a5 AC (Given)
\n\u2206ABE ~ \u2206DBC … [By AA similarity
\n\\(\\frac{B C}{B D}=\\frac{B E}{B A}\\)
\n… [In ~\u2206s, corresponding sides are proportional
\n\u2234 \\(\\frac{B C}{B D}=\\frac{B E}{B A}\\) (Hence Proved)<\/p>\n
\n\u2206ABC ~ \u2206PQR. AD is the median to BC and PM is the median to QR. Prove that \\(\\frac{\\mathbf{A B}}{\\mathbf{P Q}}=\\frac{\\mathbf{A D}}{\\mathbf{P M}}\\). (2017D)
\nSolution:
\n
\n\u2206ABC ~ \u2206PQR … [Given
\n\u22201 = \u22202 … [In ~\u2206s corresponding angles are equal
\n<\/p>\n
\nState whether the given pairs of triangles are similar or not. In case of similarity mention the criterion. (2015)
\n
\nSolution:
\n
\n(b) In \u2206PQR, \u2220P + \u2220Q + \u2220ZR = 180\u00b0 …[Angle-Sum Property of a \u2206
\n45\u00b0 + 78\u00b0 + \u2220R = 180\u00b0
\n\u2220R = 180\u00b0 – 45\u00b0 – 78\u00b0 = 57\u00b0
\nIn \u2206LMN, \u2220L + \u2220M + \u2220N = 180\u00b0 …[Angle-Sum Property of a \u2206
\n57\u00b0 + 45\u00b0 + \u2220N = 180\u00b0
\n\u2220N = 180\u00b0 – 57 – 45\u00b0 = 78\u00b0
\n\u2220P = \u2220M … (each = 45\u00b0
\n\u2220Q = \u2220N … (each = 78\u00b0
\n\u2220R = \u2220L …(each = 57\u00b0
\n\u2234 \u2206PQR – \u2206MNL …[By AAA similarity theorem<\/p>\n
\nIn the figure of \u2206ABC, D divides CA in the ratio 4 : 3. If DE || BC, then find ar (BCDE) : ar (\u2206ABC). (2015)
\n
\nSolution:
\nGiven:
\nD divides CA in 4 : 3
\nCD = 4K
\nDA = 3K
\nDE || BC …[Given
\n
\nIn \u2206AED and \u2206ABC,
\n\u22201 = \u22201 …[common
\n\u22202 = \u22203 … corresponding angles
\n\u2234 \u2206AED – \u2206ABC …(AA similarity
\n\u21d2 \\(\\frac { ar\\left( \\triangle AED \\right) }{ ar\\left( \\triangle ABC \\right) } =\\left( \\frac { AD }{ AC } \\right) ^{ 2 }\\)
\n… [The ratio of the areas of two similar triangles is equal to the square of the ratio of their corresponding sides
\n\u21d2 \\(\\\\frac { \\left( 3K \\right) ^{ 2 } }{ \\left( 7K \\right) ^{ 2 } } =\\frac { { 9K }^{ 2 } }{ { 49K }^{ 2 } } =\\frac { ar\\left( \\triangle AED \\right) }{ ar\\left( \\triangle ABC \\right) } =\\frac { 9 }{ 49 } \\)
\nLet ar(\u2206AED) = 9p
\nand ar(\u2206ABC) = 49p
\nar(BCDE) = ar (\u2206ABC) – ar (\u2206ADE)
\n= 49p – 9p = 40p
\n\u2234 \\(\\frac { ar\\left( BCDE \\right) }{ ar\\left( \\triangle ABC \\right) } =\\frac { 40p }{ 49p } \\)
\n\u2234 ar (BCDE) : ar(AABC) = 40 : 49<\/p>\n
\nIn the given figure, DE || BC and AD : DB = 7 : 5, find \\frac { ar\\left( \\triangle DEF \\right) }{ ar\\left( \\triangle CFB \\right) } [\/latex] (2017OD)
\n
\nSolution:
\nGiven: In \u2206ABC, DE || BC and AD : DB = 7 : 5.
\nTo find: \\(\\frac { ar\\left( \\triangle DEF \\right) }{ ar\\left( \\triangle CFB \\right) } \\) = ?
\n
\nProof: Let AD = 7k
\nand BD = 5k then
\nAB = 7k + 5k = 12k
\nIn \u2206ADE and \u2206ABC,
\n\u22201 = \u22201 …(Common
\n\u22202 = \u2220ABC … [Corresponding angles
\n<\/p>\n
\nIn the given figure, the line segment XY is parallel to the side AC of \u2206ABC and it divides the triangle into two parts of equal areas. Find the ratio \\(\\frac{\\mathbf{A} \\mathbf{X}}{\\mathbf{A B}}\\). (2017OD)
\n
\nSolution:
\nWe have XY || AC … [Given
\nSo, \u2220BXY = \u2220A and \u2220BYX = \u2220C …[Corresponding angles
\n\u2234 \u2206ABC ~ \u2206XBY …[AA similarity criterion
\n<\/p>\n
\nIn the given figure, AD \u22a5 BC and BD = \\(\\frac{1}{3}\\)CD. Prove that 2AC2<\/sup> = 2AB2<\/sup> + BC2<\/sup>. (2012)
\n
\nSolution:
\nBC = BD + DC = BD + 3BD = 4BD
\n\u2234 \\(\\frac{\\mathrm{BC}}{4}\\) = BD
\nIn rt. \u2206ADB, AD2<\/sup> = AB2<\/sup> – BD2<\/sup> ….(ii)
\nIn rt. \u2206ADC, AD2<\/sup> = AC2<\/sup> – CD2<\/sup> …(iii)
\nFrom (ii) and (iii), we get
\nAC2<\/sup> – CD2<\/sup> = AB2<\/sup> – BD2<\/sup>
\nAC2<\/sup> = AB2<\/sup> – BD2<\/sup> + CD2<\/sup>
\n
\n\u2234 2AC2<\/sup> = 2AB2<\/sup> + BC2<\/sup> (Hence proved)<\/p>\n
\nIn the given figure, \u2206ABC is right-angled at C and DE \u22a5 AB. Prove that \u2206ABC ~ \u2206ADE and hence find the lengths of AE and DE. (2012, 2017D)
\n
\nSolution:
\nGiven: \u2206ABC is rt. \u2220ed at C and DE \u22a5 AB.
\nAD = 3 cm, DC = 2 cm, BC = 12 cm
\nTo prove:
\n(i) \u2206ABC ~ \u2206ADE; (ii) AE = ? and DE = ?
\nProof. (i) In \u2206ABC and \u2206ADE,
\n\u2220ACB = \u2220AED … [Each 90\u00b0
\n\u2220BAC = \u2220DAE …(Common .
\n\u2234 \u2206ABC ~ \u2206ADE …[AA Similarity Criterion<\/p>\n
\n\\(\\frac{A B}{3}=\\frac{12}{D E}=\\frac{3+2}{A E}\\)
\n…..[In rt. \u2206ACB, … AB2<\/sup> = AC2<\/sup> + BC2<\/sup> (By Pythagoras’ theorem)
\n= (5)2<\/sup> + (12)2<\/sup> = 169
\n\u2234 AB = 13 cm
\n<\/p>\n
\nIn \u2206ABC, if AP \u22a5 BC and AC2<\/sup> = BC2<\/sup> – AB2<\/sup>, then prove that PA2<\/sup> = PB \u00d7 CP. (2015)
\nSolution:
\n
\nAC2<\/sup> = BC2<\/sup> – AB2<\/sup> …Given
\nAC2<\/sup> + AB2<\/sup> = BC2<\/sup>
\n\u2234 \u2220BAC = 90\u00b0 … [By converse of Pythagoras’ theorem
\n\u2206APB ~ \u2206CPA
\n[If a perpendicular is drawn from the vertex of the right angle of a triangle to the hypotenuse then As on both sides of the perpendicular are similar to the whole triangle and to each other.
\n\u2234 \\(\\frac{\\mathrm{AP}}{\\mathrm{CP}}=\\frac{\\mathrm{PB}}{\\mathrm{PA}}\\) … [In ~\u2206s, corresponding sides are proportional
\n\u2234 PA2<\/sup> = PB. CP (Hence Proved)<\/p>\n
\nABCD is a rhombus. Prove that AB2<\/sup> + BC2<\/sup> + CD2<\/sup> + DA2<\/sup> = AC2<\/sup> + BD2<\/sup>. (2013)
\nSolution:
\nGiven. In rhombus ABCD, diagonals AC and BD intersect at O.
\n
\nTo prove: AB2<\/sup> + BC2<\/sup> + CD2<\/sup> + DA2<\/sup> = AC2<\/sup> + BD2<\/sup>
\nProof: AC \u22a5 BD [\u2235 Diagonals of a rhombus bisect each other at right angles
\n\u2234 OA = OC and
\nOB = OD
\nIn rt. \u2206AOB,
\nAB2<\/sup> = OA2<\/sup> + OB2<\/sup> … [Pythagoras’ theorem
\nAB2<\/sup> = \\(\\left(\\frac{A C}{2}\\right)^{2}+\\left(\\frac{B D}{2}\\right)^{2}\\)
\nAB2<\/sup> = \\(\\left(\\frac{A C}{2}\\right)^{2}+\\left(\\frac{B D}{2}\\right)^{2}\\)
\n4AB2<\/sup> = AC2<\/sup> + BD2<\/sup>
\nAB2<\/sup> + AB2<\/sup> + AB2<\/sup> + AB2<\/sup> = AC2<\/sup> + BD2<\/sup>
\n\u2234 AB2<\/sup> + BC2<\/sup> + CD2<\/sup> + DA2<\/sup> = AC2<\/sup> + BD2<\/sup>
\n…[\u2235 In a rhombus, all sides are equal<\/p>\n
\nThe diagonals of trapezium ABCD intersect each other at point o. If AB = 2CD, find the ratio of area of the \u2206AOB to area of \u2206COD. (2013)
\nSolution:
\nIn \u2206AOB and \u2206COD, … [Alternate int. \u2220s
\n\u22201 = \u22063
\n\u22202 = \u22204
\n<\/p>\n
\nThe diagonals of a quadrilateral ABCD intersect each other at the point O such that \\(\\frac{A O}{B O}=\\frac{C O}{D O}\\). Show that ABCD is a trapezium. (2014)
\nSolution:
\n1st method.
\nGiven: Quadrilateral ABCD in which
\nAC and BD intersect each other at 0.
\nSuch that \\(\\frac{A O}{B O}=\\frac{C O}{D O}\\)
\nTo prove: ABCD is a trapezium
\nConst.: From O, draw OE || CD.
\n
\n
\nBut these are alternate interior angles
\n\u2234 AB || DC Quad. ABCD is a trapezium.<\/p>\nTriangles Class 10 Important Questions Long Answer (4 Marks).<\/h3>\n
\nIn a rectangle ABCD, E is middle point of AD. If AD = 40 m and AB = 48 m, then find EB. (2014D)
\nSolution:
\n
\nE is the mid-point of AD …[Given
\nAE = \\(\\frac{40}{2}\\) = 20 m
\n\u2220A = 90\u00b0 …[Angle of a rectangle
\nIn rt. \u2206BAE,
\nEB2<\/sup> = AB2<\/sup> + AE2<\/sup> …[Pythagoras’ theorem
\n= (48)2<\/sup> + (20)2<\/sup>
\n= 2304 + 400 = 2704
\n\u2234 EB = \\(\\sqrt{2704}\\) = 52 m<\/p>\n
\nLet ABC be a triangle and D and E be two points on side AB such that AD = BE. If DP || BC and EQ || AC, then prove that PQ || AB. (2013)
\nSolution:
\n
\nIn \u2206ABC,
\nDP || BC
\nand EQ || AC … [Given
\n
\nNow, in \u2206ABC, P and Q divide sides CA and CB respectively in the same ratio.
\n\u2234 PQ || AB<\/p>\n
\nIn the figure, \u2220BED = \u2220BDE & E divides BC in the ratio 2 : 1.
\nProve that AF \u00d7 BE = 2 AD \u00d7 CF. (2015)
\n
\nSolution:
\nConstruction:
\nDraw CG || DF
\nProof: E divides
\nBC in 2 : 1.
\n\\(\\frac{B E}{E C}=\\frac{2}{1}\\) …(i)
\n
\n<\/p>\n
\nIn the given figure, AD = 3 cm, AE = 5 cm, BD = 4 cm, CE = 4 cm, CF = 2 cm, BF = 2.5 cm, then find the pair of parallel lines and hence their lengths. (2015)
\n
\nSolution:
\n
\n<\/p>\n
\nIf sides AB, BC and median AD of AABC are proportional to the corresponding sides PQ, QR and median PM of PQR, show that \u2206ABC ~ \u2206PQR. (2017OD)
\nSolution:
\n<\/p>\n
\nProve that the ratio of the areas of two similar triangles is equal to the ratio of the squares of their corresponding sides. (2012)
\nSolution:
\nGiven: \u2206ABC ~ \u2206DEF
\n
\n
\n<\/p>\n
\nState and prove converse of Pythagoras theorem. Using the above theorem, solve the following: In \u2206ABC, AB = 6\\(\\sqrt{3}\\) cm, BC = 6 cm and AC = 12 cm, find \u2220B. (2015)
\nSolution:
\nPart I:
\nStatement: Prove that, in a triangle, if square of one side is equal to the sum of the squares of the other two sides, then the angle opposite the first side is a right angle.
\n
\nTo prove: \u2220ABC = 90\u00b0
\nConst.: Draw a right angle \u2206DEF in which DE = BC and EF = AB.
\nProof: In rt. \u2206ABC,
\nAB2<\/sup> + BC2<\/sup> = AC2<\/sup> …(i) Given
\nIn rt. \u2206DEF
\nDE2<\/sup> + EF2<\/sup> = DF2<\/sup> … [By Pythagoras’ theorem
\nBC2<\/sup> + AB2<\/sup> = DF2<\/sup>…(ii)…[\u2235 DE = BC; EF = AB
\nFrom (i) and (ii), we get
\nAC2<\/sup> = DF2<\/sup> = AC = DF
\nNow, DE = BC …[By construction
\nEF = AB …[By construction
\nDF = AC … [Proved above :
\n\u2234 \u2206DEF = \u2206ABC … (SSS congruence :
\n\u2234 \u2220DEF = \u2220ABC …[c.p.c.t.
\n\u2235 \u2220DEF = 90\u00b0 \u2234 \u2220ABC = 90\u00b0
\nGiven: In rt. \u2206ABC,
\nAB2<\/sup> + BC2<\/sup> = AC2<\/sup>
\nAB2<\/sup> + BC2<\/sup> = (6\\(\\sqrt{3}\\))2<\/sup> + (6)2<\/sup>
\n= 108 + 36 = 144 = (12)2<\/sup>
\nAB2<\/sup> + BC2<\/sup> = AC2<\/sup> \u2234 \u2220B = 90\u00b0 … [Above theorem<\/p>\n
\nIn the given figure, BL and CM are medians of a triangle ABC, right angled at A. Prove that: 4(BL2<\/sup> + CM2<\/sup>) = 5BC2<\/sup> (2012)
\n
\nSolution:
\nGiven: BL and CM are medians of \u2206ABC, right angled at A.
\nTo prove: 4(BL2<\/sup> + CM2<\/sup>) = 5 BC2<\/sup>
\nProof: In \u2206ABC, BC2<\/sup> = BA2<\/sup> + CA2<\/sup> …(i)
\nIn \u2206BAL,
\nBL2<\/sup> = BA2<\/sup> + AL2<\/sup> …[Pythagoras’ theorem
\nBL2<\/sup> = BA2<\/sup> + \\(\\left(\\frac{\\mathrm{CA}}{2}\\right)^{2}\\)
\nBL2<\/sup> = BA2<\/sup>+ \\(\\frac{\\mathrm{CA}^{2}}{4}\\)
\n\u21d2 4BL2<\/sup> = 4BA2<\/sup> + CA2<\/sup> …(ii)
\nNow, In \u2206MCA,
\nMC2<\/sup> = CA2<\/sup> + MA2<\/sup> …[Pythagoras’ theorem
\nMC2<\/sup> = CA2<\/sup>2 + \\(\\left(\\frac{\\mathrm{BA}}{2}\\right)^{2}\\)
\nMC2<\/sup> = CA2<\/sup> + \\(\\frac{\\mathrm{BA}^{2}}{4}\\)
\n4MC2<\/sup> = 4CA2<\/sup> + BA2<\/sup>
\nAdding (ii) and (iii), we get
\n4BL2<\/sup> + 4MC2<\/sup> = 4BA2<\/sup> + CA2<\/sup> + 4CA2<\/sup>+ BA2<\/sup> …[From (ii) & (iii)
\n4(BL2<\/sup> + MC2<\/sup>) = 5BA2<\/sup> + 5CA2<\/sup>
\n4(BL2<\/sup> + MC2<\/sup>) = 5(BA2<\/sup> + CA2<\/sup>)
\n\u2234 4(BL2<\/sup> + MC2<\/sup>) = 5BC2<\/sup> … [Using (1)
\nHence proved.<\/p>\n
\nIn the given figure, AD is median of \u2206ABC and AE \u22a5 BC. (2013)
\nProve that b2<\/sup> + c2<\/sup> = 2p2<\/sup> + \\(\\frac{1}{2}\\) a2<\/sup>.
\n
\nSolution:
\n
\nProof. Let ED = x
\nBD = DC = \\(\\frac{B C}{2}=\\frac{a}{2}\\) = …[\u2235 AD is the median
\nIn rt. \u2206AEC, AC2<\/sup> = AE2<\/sup> + EC2<\/sup> …..[By Pythagoras’ theorem
\nb2<\/sup> = h2<\/sup> + (ED + DC)2<\/sup>
\nb2<\/sup> = (p2<\/sup> – x2<\/sup>) + (x = \\(\\frac{a}{2}\\))2<\/sup>
\n…[\u2235 In rt. \u2206AED, x2<\/sup> + h2<\/sup> = p2<\/sup> \u21d2 h2<\/sup> = p2<\/sup> – x2<\/sup> …(i)
\nb2<\/sup> = p2<\/sup> – x2<\/sup> + x2<\/sup> + \\(\\left(\\frac{a}{2}\\right)^{2}\\)2<\/sup>+ 2(x)\\(\\left(\\frac{a}{2}\\right)\\)
\nb2<\/sup> = p2<\/sup> + ax + \\(\\frac{a^{2}}{4}\\) …(ii)
\nIn rt. \u2206AEB, AB2<\/sup> = AE2<\/sup> + BE2<\/sup> … [By Pythagoras’ theorem
\n<\/p>\n
\nIn a \u2206ABC, the perpendicular from A on the side BC of a AABC intersects BC at D such that DB = 3 CD. Prove that 2 AB2<\/sup> = 2 AC2<\/sup> + BC2<\/sup>. (2013; 2017OD)
\nSolution:
\nIn rt. \u2206ADB,
\nAD2<\/sup> = AB2<\/sup> – BD2<\/sup> …(i) [Pythagoras’ theorem
\nIn rt. \u2206ADC,
\nAD2<\/sup> = AC2<\/sup> – DC2<\/sup> …(ii) [Pythagoras’ theorem