cos(3x/2)cos(x/2)-sin(3x/2)sin(x/2)=cos(3x/2+x/2)=cos2x 怎么得出这个结果的?

证明cos 2x cos x=1/2(cos x+cos 3x) cos（x-2派/3)=-cos(x+派/3) 求不定积分cos(3x)cos(2x) 化简cos 2x (cos(x))^-2导数 cos(x^2)dx cos x>-1/2 已知sin(x)+3cos(x)=2,求sin(x)-cos(x)/sin(x)+cos(x)=? ∫ e^(3x)cos(2x) sin[cos^2(x^3+x)],求导 极限题,1.lim x-->0 cos(2x)-cos(3x)/x^22.lim x-->∞ cos(2x)-cos(3x)/x^2 2sin^2x - 5sin x cos x=3 cos^2x,求X, 2cos x (sin x -cos x)+1 y=2cos x (sin x+cos x) 化简sin(x)cos(x)cos(2x) 化简sin(x)cos(x)cos(2x) sin x cos x cos 2x 化简 化简f(x)=2cos^3 x+sin^2 (360-x)-cos(180-x)-3 / 2+2cos^2(180+x)+cos(-x)求化简图片