x + 2y + 2xy = 8
(x+1)*(2y+1) = 9
根据均值不等式,(x+1)+(2y+1) ≥ 2√[(x+1)*(2y+1)] = 2*3 = 6
所以x+2y的最小值为6-2=4
此时x=2,y=1