sin(x-20°)+cos(x+70°)+sin(x+20°)sec(70-x)=?请问有何简便解法?

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) cos(25°+x)cos(20°-x)-cos(65°-x)sin(20°-x) sin(65°-x)cos(x-20°)+cos(65°-x)cos(110°-x)=? sin(33°-x)cos(27°+x)+cos(33°-x)sin(27°+x) 求cos（20°+x）cos（25°-x）- cos（70°-x）* sin（25°-x） cos(27°+x)sin(57°+x)-sin(207°+x)sin(327°+x) 化简 sin(x-20°)+cos(x+70°)+sin(x+20°)sec(70°-x)麻烦稍微写下过程呐. sin(x-20°)+cos(x+70°)+sin(x+20°)sec(70-x)=?请问有何简便解法? 化简cos(180°+x)*sin(x+360°)/[sin(-x-180°)*cos(-180°-x)] 化简sin(x-25°)sin(65°-x)+cos(x-25°)cos(65°-x)的结果为 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°) 计算tan55°tan35°+sin（70°-x）/cos（x+20°）+1的值. 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?