f(x)=2sin^2 x+2sinxcosx =1-cos2x+sin2x =sin2x-cos2x-1 =√2sin(2x-45)-1f(x)＞0,即sin(2x-45)＞√2/2 即 45＜ 2x-45＜135 得出π/4 ＜ x＜π/2
