函数f(x）=sin^4x+cos^4x的最小正周期

因为 ( sin^2 x + cos^2 x ) ^ 2 = sin^4 x + cos^4 x + 2 sin^2 x cos^2 x所以 f(x) = ( sin^2 x + cos^2 x ) ^ 2 - 2 sin^2 x cos^2 xf(x) = 1 - 2 sin^2 x cos^2 x= 1 - 1/2 sin^2 (2x)= 1 - 1/4 * ( 1 - cos 4x ...