It is possible to see that the angle DCB is a right angle. It is also seen that sides CD and CB are congruent. So, the measure of angles CDB and CBD is the same. Since the sum of the three angles must be equal to 180°, the angle CDB must be equal to 45°.
∠CDB + ∠CBD + ∠DCB = 180°
∠CDB + ∠CBD + 90° = 180° (Replacing the value of angle DCB)
∠CDB + ∠CBD = 180° - 90° (Subtracting 90° on both sides of the equation)
∠CDB + ∠CBD = 90° (Subtracting)
2*∠CDB = 90° (Since ∠CDB = ∠CBD )
∠CDB = 90°/2 (Dividing by 2 on both sides of the equation)
∠CDB = 45°
