In △ABC\triangle ABC△ABC, if a2+b2=c2+aba^2+b^2=c^2+aba2+b2=c2+ab, find ∠C\angle C∠C.
30∘30^\circ30∘
60∘60^\circ60∘
120∘120^\circ120∘
90∘90^\circ90∘