f(x)=(sinx)^4+(cosx)^2 =[(sinx)^2]^2+(cosx)^2 =[(1-cos2x)/2]^2+(1+cos2x)/2 =[1-2cos2x+(cos2x)^2+2+2cos2x]/4 =[3+(cos2x)^2]/4 =[3+(1+cos4x)/2]/4 =(1/8)cos4x+7/8 所以周期T=2π/4=π/2. 最大值1最小值3/4
