f(x)=2sin(2x-3/π+Φ)是偶函数,则f(x)=f(-x)
即sin(2x-3/π+Φ)=sin(-2x-3/π+Φ)
则sin[2x-(3/π-Φ)]+sin[2x+(3/π-Φ)]=0
即sin2x*cos(3/π-Φ)=0对x∈R都成立
∴cos(3/π-Φ)=0 3/π-Φ=kπ+π/2