The incircle of ΔABC touches the sides BC, CA and BA at D, E and F respectively. If
AB = AC, prove that BD = CD.
Given : A circle C (O, r), in which AP and AQ are two tangents drawn from an external point A.
To prove : AP = AQ
Const. : Join O P, OQ and OA.
Proof : Since the tangent at any point of a circle is perpendicular to the radius through
the point of contact.
∴ ∠OPA = ∠OQA = 90° ...(i)
Now, in right triangles OP A and OQA, We have
OP = OQ (radii of circle)
OA = OA (common)
and ∠OPA = ∠OQA from (i)
Therefore,
ΔOPA = ΔOQA (By RHS)
This gives AP = AQ (Hence proved)
A quadrilateral ABCD is drawn to circumscribe a circle (Fig. 10.62). Prove that AB + CD = AD + BC.