If one of the angle of a triangle is equal to the sum of other two.
i.e. ∠B = ∠A + ∠C
Now, in ΔABC
Sum of all angles of triangle is 180°
∠A + ∠B + ∠C = 180°
∠B + ∠B = 180°[Therefore, ∠A + ∠C = ∠B]
2∠B = 180°
∠B = 90°
Therefore, ΔABC is right angled triangle.