1.sin（90°+33°）为什么=cos33°?2.sin63°sin123°+cos117°sin33°=?

1.
sin(π/2+α)=sin(π/2)cosα+cos(π/2)sinα=cosα
2.
sin63°sin123°+cos117°sin33°
=sin(180°-63°)sin(90°+33°)+cos117°sin33°
=sin117°cos33°+cos117°sin33°
=sin(117°+33°)
=sin150°
=sin30°
=1/2弱弱的问一下这一步=sin117°cos33°+cos117°sin33°是怎么到这一步的=sin(117°+33°)万分感谢三角函数和的展开sin(α+β)=sinαcosβ+cosαsinβ