\documentclass{article} \usepackage{amsmath} \begin{document} \begin{align*} \sqrt{x^2+y^2} &= r \\ \implies x^2+y^2 &= r^2 \end{align*} \end{document} Don't use $$ in a LaTeX document to start and end (unnumbered) display-math mode. For more on this topic, please s...