How to write parenthesis(..) in LaTeX

You can use parentheses key on the keyboard shift + (, shift + )to type parentheses in latex.

But if you use fractions in the equation, the parenthesis size will not be adjusted automatically. Below are some examples.

\documentclass{article}
\begin{document}
   $$ (a+b) $$
   $$ (a^2 + b^2) $$
   $$ (\frac{1}{a_1} + \frac{1}{a_2}) $$
\end{document}

Output :

If you use fractions or large size equations, the best method would be to write \left(arg\right) command.

This will automatically adjust the size of the parenthesis based on the size of your equation.

\documentclass{article}
\begin{document}
   $$ \left(a^2 + b^2\right) $$
   $$ \left(\frac{1}{a_1} + \frac{1}{a_2} \right) $$
   $$ \left(\frac{\frac{1}{a}}{\sin a}\right) $$
\end{document}

Output :