O is any point on the bisector of the acute angle ∠XYZ. The line OP∥ZY. Then, △YPO is an Isosceles right-angled triangle.
Isosceles but not right angled
∠POY=∠ZYO (alt.∠s)=∠PYO.
So,PY=PO.
Now, ∠XYZ<0∘
⇒POY<45∘⇒∠PYO<45∘
∴∠YPO>90∘
Hence, ΔYPO is an isosceles but not a right angled triangle.