Given,
AB = AC.
We know that angles opposite to equal sides of an isosceles triangle are equal.
∴ ∠B = ∠C = x°.
Sum of angles of triangle = 180°.
⇒ ∠A + ∠B + ∠C = 180°
⇒ 90° + x° + x° = 180°
⇒ 90° + 2x° = 180°
⇒ 2x° = 90°
⇒ x° = 45°.
Hence, ∠B = ∠C = 45°.