Let be x.

ABCD is a square.

So, DA = DC (every side of square is equal)

Therefore,

∠ACD = ∠CAD = x°

∠ACD + ∠CAD + ∠ADC= 180° (ACD is right angled triangle)

x° + x° + 90° = 180°

2 x° = 90°

x° = 45°