Strikethrough - strike out text or formula in LaTeX

Strikethrough in LaTeX using cancel packages

I personally prefer this package because it works equally well on Latex text or on Latex equations
You must use cancel packages as follows:

\cancel draws a diagonal line (slash) through its argument.
\bcancel uses the negative slope (a backslash).
\xcancel draws an X (actually \cancel plus \bcancel).
\cancelto〈value〉〈expression〉 draws a diagonal arrow through the 〈expression〉,
pointing to the 〈value〉

Here is an example I built to illustrate this package

\documentclass[12pt,a4paper]{article}
\usepackage[utf8]{inputenc}
\usepackage{cancel}
\usepackage{amsmath}
\begin{document}

I want to strike out symbols in math mode $\cancel{\alpha + 2}=8$

I want to strikethrough this \cancel{text} in text mode.

I want to strikethrough an equation

\begin{equation*} 
\cancel{f(x)=(x+a)(x+b)}
\end{equation*}

\begin{equation}
\begin{aligned}
B'&=-\nabla \times E,\\
E'&=\cancel{\nabla \times B - 2\pi j},\\
E'&=\nabla \times B - 4\pi j
\end{aligned}
\end{equation}

I prefer backslash ! Please bcancel 

\begin{equation}
\begin{aligned}
B'&=-\nabla \times E,\\
E'&=\bcancel{\nabla \times B - 2\pi j},\\
E'&=\nabla \times B - 4\pi j
\end{aligned}
\end{equation}

What about a cross ?
\begin{equation}
\begin{aligned}
B'&=-\nabla \times E,\\
E'&=\xcancel{\nabla \times B - 2\pi j},\\
E'&=\nabla \times B - 4\pi j
\end{aligned}
\end{equation}

What about cross and replace ?

\begin{equation}
\begin{aligned}
B'&=-\nabla \times E,\\
E'&=\cancelto{\nabla \times B - 2\pi j}{\nabla \times B - 4\pi j}
\end{aligned}
\end{equation}

\end{document}

Documentation in https://ctan.org/pkg/cancel

Strikethrough text in LaTeX using ulem packages

ulem is only for text. You can use sout or xout functions as follows.

\sout line struck through word

\xout marked over

\documentclass[12pt,a4paper]{article}
\usepackage[utf8]{inputenc}
\usepackage[normalem]{ulem}
\usepackage{amsmath}
\begin{document}

I want to strike out symbols in math mode $\sout{\alpha + 2}=8$

Hum hum not possible ...

I want to strikethrough this \sout{text} in text mode.

Yes we can !

I want to strikethrough this \xout{text} in text mode.

Yes we can and it is very cool xout !!!

I want to strikethrough an equation

\begin{equation*} 
\sout{f(x)=(x+a)(x+b)}
\end{equation*}

Hum hum not possible ...

\end{document}