x=2+cos@ y=1怎么消参

Sin x-sin y=2/3 cos x-cos y=1/2 求cos(x-y) 证明COS（X+Y）COS（X-Y）=COS^2X-SIN^2Y 由y=sinx怎么转变为y=5/2cos(1/2x+π/6) y=cos x^2的导数怎么求? 请问怎么证明sinX+sin(X+Y)+sin(X+2Y)/cosX+cos(X+Y)+cos(X+2Y)=tan(X+ ) y=cos(x-y) y=(sinx+cos)²+2cos²x怎么化为一角一函数, 求导y=(1+sin^2 x)/(cos(x^2)) y=cos^2x+sinx+1(|x| Y=cos（x^2+x+1)的导数 y=cos(x-2),y=1+sin"pai"x为什么是周期函数,怎么算其周期 sin(x+y)sin(x-y)=k,求cos^2x-cos^2y