Find constants $a$ and $b$ such that $\lim_\limits{x\to\infty}\left(\frac{x^2+1}{x+1}-ax-b\right)=0$.

262 Views Asked by At

Find constants $a$ and $b$ such that $\lim_\limits{x\to\infty}\left(\frac{x^2+1}{x+1}-ax-b\right)=0$.

My attempt: $\frac{x^2 + 1}{ x+1} -ax -b = \frac {x^2 +1 - (x +1)(ax+b)}{x+1}$ but then what?

2

There are 2 best solutions below

4
On BEST ANSWER

$\lim_\limits{x\to\infty}\left(\frac{x^2-1+2}{x+1}-ax+b\right)=\lim_\limits{x\to\infty}\left(\frac{x^2-1}{x+1}+\frac{2}{x+1}-ax-b\right)=\lim_\limits{x\to\infty}\left(\frac{(x+1)(x-1)}{x+1}+\frac{2}{x+1}-ax-b\right)=\lim_\limits{x\to\infty}\left(x-1+\frac{2}{x+1}-ax-b\right)=\lim_\limits{x\to\infty}\left(x-1-ax-b\right)$

From here we can find that $a=1$ and $b=-1$.

0
On

By long division,

$$\frac{x^2+1}{x+1}=x-1+\frac2{x+1},$$ where the fraction is $o(1)$.