已知cos(x-y/2)=-1/9,sin(x/2-y)=2/3,0

已知cos(x-y/2)=-1/9,sin(x/2-y)=2/3,0 Sin x-sin y=2/3 cos x-cos y=1/2 求cos(x-y) y =(cos^2) x - sin (3^x),求y' 问道三角函数题已知sin(x)-sin(y)=-(2/3);cos(x)-cos(y)=(2/3);求cos(x-y) sin(x+y)sin(x-y)=k,求cos^2x-cos^2y 化简y=sin^2(x)+2sin(x)cos(x)+3cos^2(x) 证明COS（X+Y）COS（X-Y）=COS^2X-SIN^2Y 已知x-y=派/3,且sin x-siny=1/2,求cos(x+y). 已知函数y=sin(x/2)+根号3*cos（x/2),x属于R 已知(x/a)cosθ+(y/b)sinθ=1,(x/a)sinθ-(y/b)cosθ=1,求证(x^2/a^2)+(y 已知cos^2x-cos^2y=根号3/2,则sin(x+y）·sin(x-y)的值 已知函数y=sin²x+2sinxcosx-3cos²x,x∈R