Question

In a ΔABC, if ∠A=l20° and AB = AC. Find ∠B and ∠C. 

Answer 1

Consider a Δ ABC
Given that ∠ A and AB= AC  and given to find∠ B and ∠ C
We can observe that ΔABC is an isosceles triangle since AB=AC 

⇒ ∠ B=∠C            ........................(1) [Angles opposite to equal sides are equal] 

We know that sum of angles in an isosceles triangle is equal to 180° 

∠A+∠B+∠C=180° 

∠A+∠B+∠B=180°         [from (1)] 

120° +2∠B=180 °

2∠B=180°-120 °

2∠B=60°⇒ ∠ B=30° 

∠C=∠B=30°