In a quadrilateral ABCD, ∠B=90∘,AD2=AB2+BC2+CD2, prove that ∠ACD=90∘
From Pythagoras theorem, AC2=AB2+BC2
Given that AD2=AB2+BC2+CD2
⇒AD2=AC2+CD2
Now, from converse of Pythagoras theorem, in △ ACD, angle opposite to AD is 90∘.
∴∠ACD=90∘