Question

Câu 21 nha

Answer 1

`A = [ cos 2x ] / [ sin x + cos x ]`

`A = [ cos^2 x - sin ^2 x ] / [ sin x + cos x ]`

`A = [ ( cos x - sin x ) ( cos x + sin x ) ] / [ cos x + sin x ]`

`A = cos x - sin x`

                 `-> B`