f(X)=sin(2x-π/4)-2根号2sin^2x
=√2/2sin2x-√2/2cos2x-√2(1-cos2x)
=√2/2sin2x+√2/2cos2x-√2
=sin(2x+π/4)-√2
当sin(2x+π/4)=-1时,函数有最小值 ymin=-1-√2
f(X)=sin(2x-π/4)-2根号2sin^2x
=√2/2sin2x-√2/2cos2x-√2(1-cos2x)
=√2/2sin2x+√2/2cos2x-√2
=sin(2x+π/4)-√2
当sin(2x+π/4)=-1时,函数有最小值 ymin=-1-√2