求证sin^2x+sin^2y-sin^2x*sin^2y+cos^2x*cos^2y=1

求证sin^2x+sin^2y-sin^2x*sin^2y+cos^2x*cos^2y=1 sin(x+y)sin(x-y)=k,求cos^2x-cos^2y 化简sin(2x-y)*sin y+cos(2x-y)*sin y Sin x-sin y=2/3 cos x-cos y=1/2 求cos(x-y) 化简y=sin^2(x)+2sin(x)cos(x)+3cos^2(x) y =(cos^2) x - sin (3^x),求y' 证明COS（X+Y）COS（X-Y）=COS^2X-SIN^2Y 求导y=(1+sin^2 x)/(cos(x^2)) sin^2x+cos^2y=1/2 求3sin^2x+sin^2y的最值 已知(x/a)cosθ+(y/b)sinθ=1,(x/a)sinθ-(y/b)cosθ=1,求证(x^2/a^2)+(y 设sin(x+y)sin(x-y)=m,则cos^2x-cos^2y的值 tan(x+y)tan(x-y)=sin^2x-sin^2y/cos^2x-sin^2y 顺便问一下. tan,sin,