sin(2x+φ)要成为偶函数,只有化为±cos(2x)
sin(2x+φ)＝cos(π/2－2x－φ)＝cos(2x+φ－π/2)
所以φ＝kπ＋π/2,k为任意整数.由0＜φ＜π得k＝0,所以φ＝π/2