A=[a_{i,j}]_{2X2 }matrix a_{11}=2, a_{12}=1, a_{21}=-1, a_{22}=0 find the U unitary matrix for A and also U^{*}AU matrix must be triangular matrix?

This is linear algebra question i forgot this subject and i don't have any math book about linear algebra. Please solve this question with how do you solved i must learn this question's algorithm. And my english isn't good. please use basic clauses. Thanks now.