The denominator limit of (1) is 0. If the fractional limit exists, the molecular limit is 0.

According to Roberta's law, the original formula = lim.

Then a = -7.

lim & ltx→ 1 & gt； (x^2-7x+b) = -6+b = 0，b = 6。

(2) Original formula = lim

= lim & ltx→∞& gt； [( 1-a)x^2-(a+b)x+ 1-b]/(x+ 1)

= lim & ltx→∞& gt； [( 1-a)x-(a+b)+( 1-b)/x]/( 1+ 1/x)= 0

Then 1-a = 0 and a+b= 0. a = 1，b = - 1。