y=2sin2x值域为[-2,1]所以 2sin2x=-2 sin2x=-1 2x=2kπ+3π/2 x=kπ+3π/42sin2x=1 sin2x=1/2 2x=2kπ+π/6 或=2kπ+5π/6 x=kπ+π/12或=kπ+5π/12因为[a,b]内的取值没有2x=2kπ+π/2 所以x没有kπ+π/4所以 a=kπ...