x2>x1>-1 f(x2)-f(x1)=(x2)^2-(x1)^2+2(x2-x1)
=(x2-x1)(x2+x1+2)
x2>x1>-1 -->x2-x1>0 x2+x1+2>0
-->f(x2)-f(x1)>0 -->在(-1,+∞)是增函数