In which of the following quadrilaterals, a diagonal is not an angle bisector?
Rectangle
In the case of a rectangle, the diagonal is not an angle bisector.
Consider a rectangle ABCD.
Here, ∠ ADB = ∠ DBC (Alternate angles)
But, ∠ DBC is not equal to ∠ BDC (Angles opposite to unequal sides of a triangle are unequal)
∴ ∠ ADB is not equal to ∠ BDC
So, diagonal DB does not bisect ∠ D.