Plane Geometry


  1. If P and Q are the mid points of the sides CA and GB respectively of a triangle ABC, right-angled at C. Then the value of 4 (AQ2 + BP2) is equal to :











  1. View Hint View Answer Discuss in Forum

    From given figure , we have
    AQ2 = AC2 + QC2
    BP2 = BC2 + CP2
    AQ2 + BP2 = (AC2 + BC2) + (QC2 + CP2) = AB2 + PQ2.

    ∴ AQ2 + BP2 = AB2 +1AB×1AB∵ PQ =1AB
    222
    AQ2 + BP2 = 5AB2 ⇒ 4(AQ2 + BP2) = 5AB2
    4


    Correct Option: B

    From given figure , we have
    AQ2 = AC2 + QC2
    BP2 = BC2 + CP2
    AQ2 + BP2 = (AC2 + BC2) + (QC2 + CP2) = AB2 + PQ2.

    ∴ AQ2 + BP2 = AB2 +1AB×1AB∵ PQ =1AB
    222
    AQ2 + BP2 = 5AB2 ⇒ 4(AQ2 + BP2) = 5AB2
    4



  1. In a triangle ABC, ∠A = x°, ∠B = y° and ∠C = (y + 20)°. If 4x – y = 10, then the triangle is :









  1. View Hint View Answer Discuss in Forum

    Given :- ∠A = x° , ∠B = y° , ∠C = ( y + 20 )° and 4x – y = 10
    We know that , ∠A + ∠B + ∠C = 180°
    ⇒ x + y + ( y + 20 ) = 180°
    ⇒ x + 2y = 180 - 20 = 160° ........... ( ⅰ )
    4x – y = 10 ........... ( ⅱ )
    From ( ⅰ ) and ( ⅱ ) , we get
    ⇒ y = 70 , x = 20
    ∴ The angles of the triangle are 20° , 70° , 90° .
    Hence , the triangle will be Right-angle triangle .

    Correct Option: A

    Given :- ∠A = x° , ∠B = y° , ∠C = ( y + 20 )° and 4x – y = 10
    We know that , ∠A + ∠B + ∠C = 180°
    ⇒ x + y + ( y + 20 ) = 180°
    ⇒ x + 2y = 180 - 20 = 160° ........... ( ⅰ )
    4x – y = 10 ........... ( ⅱ )
    From ( ⅰ ) and ( ⅱ ) , we get
    ⇒ y = 70 , x = 20
    ∴ The angles of the triangle are 20° , 70° , 90° .
    Hence , the triangle will be Right-angle triangle .



  1. In a circular lawn, there is a 16 m long path in the form of a chord. If the path is 6 m away from the center of the lawn, then find the radius of the circular lawn.











  1. View Hint View Answer Discuss in Forum

    From given figure , we can see that
    Let AB = 16 m , OM = 6 m , AM = BM = 8 m and OA = r
    In triangle AMO ,
    By pythagoras theorem ,
    OA2 = AM2 + OM2

    Correct Option: C

    From given figure , we can see that
    Let AB = 16 m , OM = 6 m , AM = BM = 8 m and OA = r
    In triangle AMO ,
    By pythagoras theorem ,
    OA2 = AM2 + OM2
    OA2 = 82 + 62 = 64 + 36
    OA2 = 100 ⇒ OA = √ 100 = 10
    ∴ OA = r = 10 m
    The radius of the circular lawn = 10 m



  1. Of all the chords of a circle passing through a given point in it, the smallest is that which :









  1. View Hint View Answer Discuss in Forum

    Let C(O, r) is a circle and let M is a point within it where O is the centre and r is the radius of the circle.
    Let CD is another chord passes through point M.
    We have to prove that AB < CD.
    Now join OM and draw OL perpendicular to CD.
    In right angle triangle OLM,
    OM is the hypotenuse.
    So OM > OL

    Correct Option: D

    Let C(O, r) is a circle and let M is a point within it where O is the centre and r is the radius of the circle.
    Let CD is another chord passes through point M.
    We have to prove that AB < CD.
    Now join OM and draw OL perpendicular to CD.
    In right angle triangle OLM,
    OM is the hypotenuse.
    So OM > OL
    ⇒ chord CD is nearer to O in comparison to AB.
    ⇒ CD > AB
    ⇒ AB < CD
    So all chords of a circle of a circle at a given point within it, the smallest is one which is bisected at that point.
    Hence required answer will be option D .



  1. ABCD is a parallelogram and X, Y are the mid-points of sides AB and CD respectively. Then quadrilateral AXCY is a :













  1. View Hint View Answer Discuss in Forum

    ABCD is a parallelogram and AXCY is a quadrilateral .
    Since X and Y are the mid-points of AB and DC respectively.

    ∴ AX =1AB and CY = 1DC
    22

    Correct Option: A

    ABCD is a parallelogram and AXCY is a quadrilateral .
    Since X and Y are the mid-points of AB and DC respectively.

    ∴ AX =1AB and CY = 1DC
    22
    But ∴ AB = DC ⇒1AB =1DC ⇒ AX = CY
    22

    Also, AB || DC [∴ ABCD is a parallelogram]
    ⇒ AX || YC
    Thus, in quadrilateral AXCY,
    AX || YC and AX = YC
    Hence, quadrilateral AXCY is a parallelogram.In which the opposite sides are equal and parallel.