Plane Geometry


  1. In the given figure, side BC of Δ ABC is produced to form ray BD and CE || BA. Then ∠ ACD is equal to :













  1. View Hint View Answer Discuss in Forum

    From above given figure , we can see that
    CE || BA and AC is the transversal.
    ∴ ∠4 = ∠1 (alternate interior ∠s) .......... ( 1 )
    Again, CE || BA and BD is the transversal.
    ∴ ∠5 = ∠2 (corresponding ∠s) ................( 2 )

    Correct Option: C

    From above given figure , we can see that
    CE || BA and AC is the transversal.
    ∴ ∠4 = ∠1 (alternate interior ∠s) .......... ( 1 )
    Again, CE || BA and BD is the transversal.
    ∴ ∠5 = ∠2 (corresponding ∠s) ................( 2 )
    Adding equations ( 1 ) and ( 2 )
    ∴ ∠4 + ∠5 = ∠1 + ∠2
    ∴∠ACD = ∠A + ∠B.


  1. In fig, AB = AC, D is a point on AC and E on AB such that AD = ED = EC = BC. Then ∠A : ∠B :













  1. View Hint View Answer Discuss in Forum

    As per given figure , we can see that
    In ΔBCE, BC = EC, ∴ ∠B = ∠BEC
    In ΔCDE, ED = EC, ∴ ∠ECD = ∠EDC
    and In ΔADE, AD = ED, ∴ ∠AED = ∠A
    Now ∠B = ∠BEC = ∠A + ∠ECD = ∠A + ∠EDC = ∠A + ∠EAD + ∠AED
    { ∴ ∠EDC = ∠EAD + ∠AED }
    =∠A + ∠A + ∠A = 3∠A { By ASA property }

    Correct Option: D

    As per given figure , we can see that
    In ΔBCE, BC = EC, ∴ ∠B = ∠BEC
    In ΔCDE, ED = EC, ∴ ∠ECD = ∠EDC
    and In ΔADE, AD = ED, ∴ ∠AED = ∠A
    Now ∠B = ∠BEC = ∠A + ∠ECD = ∠A + ∠EDC = ∠A + ∠EAD + ∠AED
    { ∴ ∠EDC = ∠EAD + ∠AED }
    =∠A + ∠A + ∠A = 3∠A { By ASA property }

    ∠B=∠3
    ∠A1

    ⇒ ∠A : ∠B = 1 : 3.



  1. PQRS is a square. The ∠ SRP is equal to :













  1. View Hint View Answer Discuss in Forum

    PQRS is a square .
    We know that Every angle of square is 90° and the diagonals bisect each other at right angles .
    SP = SR and ∠S = 90°

    Correct Option: A

    PQRS is a square .
    We know that Every angle of square is 90° and the diagonals bisect each other at right angles .
    SP = SR and ∠S = 90°

    and ∠SRP = ∠SPR =1(90°) = 45°
    2

    Hence, ∠SRP = 45°.


  1. The two sides of a right triangle containing the right angle measure 3 cm and 4 cm. The radius of the in circle of the triangle is :











  1. View Hint View Answer Discuss in Forum

    If the in circle of a triangle ABC touches BC at D, then |BC - CD| = |AB - AC|
    In our case, AC = 5, AB = 3
    ⇒ AC – AB = 2
    ∴ CD – BD = 2


    Correct Option: C

    First method :-
    If the in circle of a triangle ABC touches BC at D, then |BC - CD| = |AB - AC|
    In our case, AC = 5, AB = 3
    ⇒ AC – AB = 2
    ∴ CD – BD = 2
    In our case, BC = 4
    ⇒ BD + BD = 4 and – BD + DC = 22
    ⇒ CD = 3
    ⇒ BD = 1 = OE = Radius of the in circle.
    second method :-
    We know that , In right angle triangle
    Here , a = 3 cm , b = 4 cm and c = 5 cm
    We know that ,

    The radius of the incircle = a + b - c
    2

    The radius of the incircle = 3 + 4 - 5 = 2
    22

    ∴ The radius of the incircle = 1 cm




  1. If one of the diagonals of a rhombus is equal to its side, then the diagonals of the rhombus are in the ratio :











  1. View Hint View Answer Discuss in Forum

    Let ABCD is a rhombus in which AB = BC = CD = DA = diagonal CA.
    In triangle ABC ,
    AB = BC = CA , therefore ∠B = 60°
    ∠D = ∠B = 60°
    ∠A=180 - ∠B = 180° - 60° =120°
    ∠C = ∠A=120°
    Hence ,The ratio of diagonals = √2 : 1

    Correct Option: B

    Let ABCD is a rhombus in which AB = BC = CD = DA = diagonal CA.
    In triangle ABC ,
    AB = BC = CA , therefore ∠B = 60°
    ∠D = ∠B = 60°
    ∠A=180 - ∠B = 180° - 60° =120°
    ∠C = ∠A=120°
    Hence ,The ratio of diagonals = √2 : 1