（1）f(x)=sin2x-1+cos2x=√2sin(2x+π/4)-1
最小正周期T=2π/2=π
（2）f(x)=√2sin(2x+π/4)-1最大值为√2-1
此时2x+π/4=2kπ+π/2
x=kπ+π/8 (k∈Z)