(x+2)(x+5)=(x+3.5)^2-2.25
(√（(x+2）(x+5)）-|x+3.5|)(√（(x+2）(x+5)）+|x+3.5|)=-2.25
lim(x→-∞)[（√（(x+2）(x+5)）-|x+3.5|]
=lim(x→-∞)[-2.25/[√（(x+2）(x+5)）+|x+3.5|)]]
=0
于是
lim(x→-∞)[（√（(x+2）(x+5)）+x]=-3.5