I recently found the package witharrows which allows you to annotate your equations and steps taking during algebraic manipulations and things like this for example.
\WithArrowsOptions{displaystyle,tikz=blue}
$\begin{WithArrows}
\sum_{i=1}^n (x_i+1)^2
& = \sum_{i=1}^n (x_i^2+2x_i+1) \Arrow{by linearity}\\
& = \sum_{i=1}^n x_i^2 + 2\sum_{i=1}^nx_i+ n
\end{WithArrows}$
Would generate
I also like to use the gather environment to show manipulations to both sides of an equation (using the gather environment)
I was wondering if anyone has any suggestions as to how I can annotate/use arrows to show algebraic manipultations inside the gather environment
tikzmark
.witharrows
. However, I will try to write a new version of the extensionwitharrows
to face this problem (I'm the author of that extension).