sin(65°-x)cos(x-20°)+cos(65°-x)cos(110°-x)=?

cos(25°+x)cos(20°-x)-cos(65°-x)sin(20°-x) sin(65°-x)cos(x-20°)+cos(65°-x)cos(110°-x)=? 化简sin(x-25°)sin(65°-x)+cos(x-25°)cos(65°-x)的结果为 为什么cos(20°+x) = sin(70°-x)cos(25°-x) = -cos(155°+x)?这两步没怎么看懂.cos(20+x)cos(25-x)-sin(20-x)sin(25-x)cos(20+x)cos(25-x)-sin(20+x)sin(25-x)20，25都是度数 求cos(20°+x)cos(25°-x)-cos(70°-x)sin(155°+x) sin(33°-x)cos(27°+x)+cos(33°-x)sin(27°+x) cos(27°+x)sin(57°+x)-sin(207°+x)sin(327°+x) 化简cos(180°+x)*sin(x+360°)/[sin(-x-180°)*cos(-180°-x)] 数学、急cos(x+27°)cos(18°-x)-sin(18°-x)sin(x+27°)等于多少 求值：sin(10°+x)cos(50°-x)+sin(50°-x)cos(10°+x) sin(x+105°)cos(x-15°)-cos(x+105°)sin求化简 sin(x+105°)cos(x-15°)-cos(x+105°)sin(x-15°) 求cos（20°+x）cos（25°-x）- cos（70°-x）* sin（25°-x） 表示度.sin（65-x）cos（x-20）+cos（65-x）cos（110-x） 函数Y=4cos(x-20°)+3sin(x+10°)的最大值 cos x/sin x+sin x/(1+cos x) 化简. sin（sin（sin（sin（x）=cos（cos（cos（cos（x）,X等于多少? cos x /sin x= cos(x+27°)cos(18°-x)-sin(18°-x)sin(x+27°)=cos(x+27°)cos(18°-x)+cos[90°-(60°-x)]sin(x-18°)原本是-sin(18°-x)负号怎么变成的+cos[90°-(60°-x)] cos前的负号