Plane Geometry


  1. Suppose that the medians BD, CE and AF of a triangle ABC meet at G. Then AG : GF is









  1. View Hint View Answer Discuss in Forum

    We draw a figure triangle ABC whose the medians BD, CE and AFmeet at point G ,

    Point G is the centroid of ∆ ABC.
    Point G divides AF (each median) in the ratio 2 : 1.
    Proof :-

    Reflect ∆ ABC on side AC.
    ABCB1 is a parallelogram.
    BEB1 is a straight line. and
    ∵ CD = AD, and CD || AD1
    DCD1A is a parallelogram.
    DG || CG1

    Correct Option: B

    We draw a figure triangle ABC whose the medians BD, CE and AFmeet at point G ,

    Point G is the centroid of ∆ ABC.
    Point G divides AF (each median) in the ratio 2 : 1.
    Proof :-

    Reflect ∆ ABC on side AC.
    ABCB1 is a parallelogram.
    BEB1 is a straight line. and
    ∵ CD = AD, and CD || AD1
    DCD1A is a parallelogram.
    DG || CG1
    ∵ BD = DC and DG || CG, and BG = GG1
    ∴ BG : GG1 = 1 : 1
    ∵ GE = EG1, BG = GE = 2 : 1


  1. AD is the median of ∆ ABC. If O is the centroid and AO = 10 cm, then OD is









  1. View Hint View Answer Discuss in Forum

    We draw a figure triangle ABC whose the side AD is the median and O is the centroid ,

    Here , AO = 10 cm
    Point O, is the centroid of ∆ ABC.
    AO : OD = 2 : 1

    10
    =
    2
    ⇒ 2 × OD = 10
    OD1

    Correct Option: A

    We draw a figure triangle ABC whose the side AD is the median and O is the centroid ,

    Here , AO = 10 cm
    Point O, is the centroid of ∆ ABC.
    AO : OD = 2 : 1

    10
    =
    2
    ⇒ 2 × OD = 10
    OD1

    ⇒ OD =
    10
    = 5 cm.
    2



  1. Possible lengths of the three sides of a triangle are :









  1. View Hint View Answer Discuss in Forum

    We know that the sum of two sides of a triangle is greater than the third side.
    Clearly,
    3 + 4 > 5
    4 + 5 > 3
    5 + 3 > 4

    Correct Option: B

    We know that the sum of two sides of a triangle is greater than the third side.
    Clearly,
    3 + 4 > 5
    4 + 5 > 3
    5 + 3 > 4
    Therefore , Possible lengths of the three sides of a triangle are 3 cm, 4 cm and 5 cm .


  1. In ∆ ABC, AB = a – b, AC = √a² + b² and BC = √2ab, then find angle B.









  1. View Hint View Answer Discuss in Forum

    According to question , we draw a figure

    Given , AB = a – b; BC = √2ab ;
    AC = √a² + b²
    ∴ AB² + BC² = (a – b)² + (√2ab

    Correct Option: C

    According to question , we draw a figure

    Given , AB = a – b; BC = √2ab ;
    AC = √a² + b²
    ∴ AB² + BC² = (a – b)² + (√2ab
    AB² + BC² = a² + b² – 2ab + 2ab = a² + b² = AC²
    ∴ ∠ABC = 90°



  1. BD and CE are two medians of the triangle ABC. If EO = 7cm, then the length of CE is









  1. View Hint View Answer Discuss in Forum


    Given that , EO = 7cm,
    Point ‘O’ is the centroid of triangle ABC.

    ∴ OE =
    1
    CE
    3

    Correct Option: C


    Given that , EO = 7cm,
    Point ‘O’ is the centroid of triangle ABC.

    ∴ OE =
    1
    CE
    3

    ⇒ 7 =
    1
    CE
    3

    ∴ CE = 7 × 3 = 21 cm