已知函数的极限是参数的值。

=(x→∞)lim[(x？-1+2)/(x+1)-ax-b]

=(x→∞)lim {[(x+1)(x-1)+2]/(x+1)-ax-b }

=(x→∞)lim[x-1+2/(x+1)-ax-b]

=(x→∞)lim[(1-a)x-(1+b)]

=4

1-a=0，-(1+ b)=4

a=1，b=-5