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Home Aptitude Plane Geometry Comments

  • Question
  • If ABCD is a parallelogram and AC and BD be its diagonals, then:


  • Options
  • A. AB2 + BC2+ CD2+ DA2 = AC2 ? BD2
  • B. AB2 + BC2+ CD2 + DA2 = AC2 + BD2
  • C. 4AD2 = 2AC2 + 2BD2
  • D. 4AB2 = 2AC2 ? 2BC2

  • Correct Answer
  • AB2 + BC2+ CD2 + DA2 = AC2 + BD2 

    Explanation

    In ||gm ABCD , we have
    Since diagonals of parallelogram(||gm ) bisect each other,
    ? M will be the mid-point of each of the diagonal AC and BD
    ? In ?ABC AB2 + BC2 = 2(AM2 + MB2) ......... ( 1 ) [Appolonius Theorem]
    In ?ADC AD2 + CD2 = 2(AM2 + DM2) ......... ( 2 )
    = 2(AM2 + MB2) [? DM = BM]
    Adding equations ( 1 ) and ( 2 )
    AB2 + BC2 + CD2 + DA2 = 2(AM2 + MB2 + 2(AM2 + MB2 = 4AM2 + 4MB2
    = (2AM)2 + (2MB)2= AC2+ BD2. { ? AM = MC , MB = MD }


  • Plane Geometry problems


    Search Results


    • 1. 
      In a right angled ? ABC, Right angled at A, AD ? BC. Then :

    • Options
    • A. AD2 = BD × CD
    • B. AD2 = AB × AC
    • C. AD2 = BD × AB
    • D. AD2 = CD × AC
    • Discuss
    • 2. 
      A vertical stick 12 cm long casts a shadow 8 cm long on the ground. At the same time a tower casts the shadow 40 m long on the ground. Find the height of the tower.

    • Options
    • A. 600 m
    • B. 160 m
    • C. 60 m
    • D. 52 m
    • Discuss
    • 3. 
      In, ?ABC, D and E are the mid-points of AB and AC respectively. Find the ratio of the areas of ?ADE and ?ABC.

    • Options
    • A. 1 2
    • B. 1 4
    • C. 3 4
    • D. 1 8
    • Discuss
    • 4. 
      In the given figure, find the length of BD.

    • Options
    • A. 13.5 cm
    • B. 12 cm
    • C. 14.5 cm
    • D. 15 cm
    • Discuss
    • 5. 
      In the given figure ?QPR = 90°, QR = 26 cm, PM = 6 cm, MR = 8 cm and ?PMR = 90°, find the area of ?PQR.

    • Options
    • A. 180 cm2
    • B. 240 cm2
    • C. 120 cm2
    • D. 150 cm2
    • Discuss
    • 6. 
      In the given figure, DE || BC and DE : BC = 3 : 5 the ratio of the areas of ? ADE and the trapezium BCED.

    • Options
    • A. 9 25
    • B. 12 25
    • C. 3 4
    • D. 9 16
    • Discuss
    • 7. 
      In a ? ABC, AD intersects ? A and BC. If BC = a, AC = b and AB = c, Then :

    • Options
    • A. CD = b+c ab
    • B. CD = ab b+c
    • C. CD = bc+ab ac
    • D. CD = ac cb+ab
    • Discuss
    • 8. 
      In the given figure DE||BC and AD : DB = 5 : 4,
      Then ar(?DFE)
      ar(?CFB)

    • Options
    • A. 25 81
    • B. 25 16
    • C. 16 25
    • D. 16 81
    • Discuss
    • 9. 
      In center of a triangle lies in the interior of :

    • Options
    • A. an isosceles triangle only
    • B. any triangle
    • C. an equilateral triangle only
    • D. a right triangle only
    • Discuss
    • 10. 
      In the given figure, which of the following is true :

    • Options
    • A. x = ? + ? + ?
    • B. x + ? = ? + ?
    • C. x + ? = ? + ?
    • D. x + ? = ? + ?
    • Discuss


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