f(x)=(ax+2a-2a+1)/(x+2)
=a+(-2a+1)/(x+2)
要使函数在区间(-2,+无穷)单调递增,因为1/(x+2)在区间(-2,+无穷)单调递减,所以1-2a必须小于0(减减为增),得a>0.5