反函数法1-x=2xy+5y2xy+x=1-5yx(1+2y)=(1-5y)x=(1-5y)/(1+2y)1+2y≠0y≠-1/2值域{y|y≠-1/2}
y=(1-x)/(2x+5)1-x = y（2x+5)1-x = 2yx+5y-x-2yx = 5y-1x = （1-5y)/(2y+1)2y+1≠0y≠-1/2值域（-∞，-1/2)，(-1/2，+∞）
