In a quadrilateral ABCD, ∠B = 90° and AD 2 = AB 2 + BC 2 + CD 2, then ∠ACD is equal to:

In a quadrilateral ABCD,
Given :- ∠B = 90°
AB² + BC² + CD² = AC² + CD² = AD² { ∴ In triangle ABC , AB² + BC² = AC² }
So, in triangle ACD, angle opposite to AD = 90° ( by Converse of Pythagoras theorem)
⇒ ∠ACD = 90°