由函数图像性质知当2x+π/4=2kπ+π/2即x=kπ+π/8时f（x）的值最大f(x)=根号2*1+1=根号2+1
当2x+π/4=2kπ+3π/2即x=kπ+5π/8时f（x）的值最小f(x)=根号2*-1+1=1-根号2