sin^4x+cos^4x-2cos^2x的周期,最值

sin^4x+cos^4x-2cos^2x=[(sinx)^2+(cosx)^2]^2-2(sinx)^2(cosx)^2-2(cosx)^2=1-(1/2)[sin(2x)]^2-1-cos(2x)=-(1/2)[1-cos(2x)^2]-cos(2x)=(1/2)[(cos(2x)^2-2cos(2x)-1]=(1/2)[cos(2x)-1]^2-1周期=π,cos(2x)=-1时有...