f(x)=√(x^2+x-6)
=√(x^2+x+1/4-6-1/4)
=√(x+1/2)^2-25/4
(x+1/2)^2-25/4>＝0
(x+1/2)^2>=25/4
x+1/2>=5/2 或 x+1/2=2 或 x=2时为增函数,x