sin 2α= = ; cos 2α= = ; 1+sin 2α=(sin α+cos α)2; 1-sin 2α=(sin α-cos α)2; (sin α+cos α)2+(sin α-cos α)2=2; 1±sin α= ; tan = = . 2.辅助角公式 asin α+bcos α= sin(α+φ),