△ABC is an isosceles triangle, in which AB=AC. Side BA is produced to D such that AD=AB. ∠BCD is equal to ___.
90∘
Given, AB=AC and BA=AD
In △ABC,
∠ABC = ∠ACB = x (opposite angles of equal sides)
In △ACD,
∠ADC = ∠ACD = y (opposite angles of equal sides)
In △BCD,
∠DBC + ∠BCD + ∠CDB= 180∘
x + x + y +y = 180∘
2x+2y = 180∘
x+y = 90∘
∠BCD = (x+y) = 90∘
∠BCD = 90∘