How to use less-than or equivalent To(≲) symbol in LaTeX?

There is no default command to print the less-than or equivalent to symbol to a LaTeX document.

For this you need the amssymb package, this package provides a command called \lesssim which allows you to print this symbol in the document.

\documentclass{article}
\usepackage{amssymb}
\begin{document}
   \[ a \lesssim b \]
   \[ x_1 \lesssim x_2 \]
   \[ \frac{1}{a_1} \lesssim \frac{1}{a_2} \]
\end{document}

Output :

• Less than or equal to(≤) symbol in LaTeX
• Not Less Than(≮) symbol in LaTeX
• Less than over not equal to(≨) symbol in LaTeX
• Less-Than or Slanted Equal To(⩽) symbol in LaTeX