# <span lang="EN-US

Let in Δ ABC,

A = 60°

It is given that triangle is a isosceles triangle.

Case 1

Two equal angles both equal to 60°

If it happens, then sum of two equal angles will be = 60 + 60 = 120°

But, sum of all angles of a triangle is 180°

Thus, the third angle = 180-120 = 60

Hence, other two angles are 60° each.

Case 2

Two equal angles other than given angle (A)

If A = 60°

Let B = C = y°

Sum of all angles of a triangle is 180°

A + B + C = 180°

60 + y + y = 180°

60 + 2y = 180°

2y = 180-60

= 120 Hence the other 2 angles are also 60°

Hence, in both the cases the triangle is equilateral (each angle = 60°)

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