Question

in triangle ABC, angle A=100 degrees and AB=AC,find angleA and angle B

Answer 1

Angle A= 100..... as already given
Angle B= 40.....as AB=AC i.e Angle B=Angle C
And we know
AngA+ AngB+AngC=180
so 2AngB=180-100
and finally AngB=40

Answer 2

Given

In  ΔABC

∠A=100°  and  AB=AC.

Find the  ∠A and ∠B

To proof

As given in the question

AB=AC

Two sides of the triangle are equal than its become an isosceles triangle.

In the isosceles triangle if the two sides are equal than their opposite angles are also equal.

thus

∠ A = ∠B

Let us assume that the value of ∠ A = ∠B be x.

in ΔABC

∠A +∠B +∠ C = 180°

x + 100 + x  = 180 °

2x = 180 -100

2x = 80

$x = \frac{80}{2}$

x = 40°

therefore ∠ A = ∠B = 40°

Hence proved