latex mcq questions

Question 1)

\begin{align*}
\lim_{a\to 0}\frac{-b\pm\sqrt{b^2-4ac}}{2a} &= \lim_{a\to 0}\frac{b^2-(b^2-4ac)}{2a\left(-b\mp\sqrt{b^2-4ac}\right)}\\
&= \lim_{a\to 0}\frac{2c}{-b\mp\sqrt{b^2-4ac}}.
\end{align*}

Question 2)

x = {-b \pm \sqrt{b^2-4ac} \over 2a}

Question 3)

\rm z\ =\ \dfrac{1}{x}\ =\ \dfrac{-b \pm \sqrt{b^2-4\:a\:c}}{2\:c}