cos^4x-sin^4x=cos2x 为什么

cos^4x-sin^4x=cos2x 为什么 cos2x=3/5.sin^4+cos^4x=? cos2x=cos^x-sin^x 为什么? 求证（cos^2x-sin^2x)(cos^4x+sin^4x）+1/4sin2xsin4x=cos2x 化简f (x)=2cos2x+sin2x-4cox要有过程……2cos2x+sin^2x-4cos 函数y=cos^4x-sin^4x的最小正周期y=(cos^2x+sin^2x)(cos^2x-sin^2x)为什么等于cos^2x-sin^2x=cos2x谢谢 若cos2x=√2/3,则cos^4x+sin^4x=多少? 设sin(π/4-x)=5/13,则cos2x/cos(π/4+x)=_______ 设sin(π/4-x)=5/13,则cos2x/cos(π/4-x)=_______ sin^4 x+cos^4 x=?以(i)cos2x表示.(ii)sin2x表示 如果cos2x=a,那么sin^4x+cos^4x的值等于? tanx=-1/2,sin2x+cos2x/4cos^2x-3sin^2x+1= 求证!cos^8x-sin^8x+1/4sin2xsin4x =cos2x cos^4(x)-sin^4(x)等于?是cos^2(x)还是cos2x ：求证:(cos^2x-sin^2x)(cos^4x+sin^4x)+1/4sin2xsin4x=cos2x求证:(cos^2x-sin^2x)(cos^4x+sin^4x)+1/4sin2xsin4x=cos2x我算到右边=cos2x（1-sin^2xcos^2x） 接下来该怎么办? ：求证:(cos^2x-sin^2x)(cos^4x+sin^4x)+1/4sin2xsin4x=cos2x求证:(cos^2x-sin^2x)(cos^4x+sin^4x)+1/4sin2xsin4x=cos2x我算到右边=cos2x（1-sin^2xcos^2x） 接下来该怎么办? 已知函数f(x)=(6cos^4x+5sin^2x-4)/cos2x 判断f(x)的奇偶性 如果cos2x=3/5.那么sin^4+cos^4x=多少