Question

∆ABC, BC = AB and angleB = 80° , then angleA is equal to

Answer 1

in ∆ ABC
AB = BC

=> angle A = angle C ( angles opposite to equal sides are equal)
let us suppose angle A x


by angle sum property of triangles ,

=> angle A + angle B + angle C = 180°
=> x +80°+x = 180°
=> 2x = 100°

=> x = 100/2 => 50°

angle A = 50°


hope this helps