ABC is a right triangle with AB = AC. Bisector of A meets BC at D. Prove that BC = 2 AD.
Given : ABC is a right triangle AB = AC
Bisector of A meets BC at D.
To prove : BC = 2AD
Proof : In ABC, AB = AC (given)
Then B = C (If sides are equal in a triangle, then opposite angle are also equal)
Now,
BAC + ABC + BCA = 180° (angle sum property)
90° + 2ABC = 180° (Q ABC = ACB)
B = 45° = ACB
BAD = CAD (AD is bisector ÐA)
BD = AD, CD = AD (Sides opposite to equal angles are equal).
Adding both,
BD + CD = AD + AD
BC = AD + AD
BC = 2AD ( BD + DC = BC)
Hence Proved.