2cos(3x+π/4)-√2=0
cos(3x+π/4)=√2/2
3x+π/4=2kπ+π/4
x=2kπ/3
x∈【0,2π)
k=0,x=0
k=1 ,x=2π/3
k=2,x=4π/3
k=3,x=2π (舍）