Giúp mik với cần gấp ạ Please

$a)\quad \lim\dfrac{\sqrt{n^2+ n-1} - \sqrt{4n^2-2}}{n+3}$

$=\lim\dfrac{\sqrt{1 +\dfrac1n - \dfrac{1}{n^2}} - \sqrt{4 -\dfrac{2}{n^2}}}{1+\dfrac3n}$

$=\dfrac{\sqrt{1 + 0-0} - \sqrt{4-0}}{1+0}$

$= -1$

$b)\quad \lim\left(\sqrt{n^2-1} - \sqrt{n^2+2}\right)$

$= \lim\dfrac{\left(\sqrt{n^2-1} - \sqrt{n^2+2}\right)\left(\sqrt{n^2-1} + \sqrt{n^2+2}\right)}{\sqrt{n^2-1} + \sqrt{n^2+2}}$

$= \lim\dfrac{-3}{\sqrt{n^2-1} + \sqrt{n^2+2}}$

$=\lim\dfrac{-\dfrac3n}{\sqrt{1 -\dfrac{1}{n^2}} +\sqrt{1 +\dfrac{2}{n^2}}}$

$=\dfrac{0}{\sqrt{1-0} + \sqrt{1+0}}$

$= 0$