Question: I have the following MWE

```
\documentclass[10pt, a4paper]{article}
\usepackage{amsfonts, amsmath, amssymb, amsfonts}
\begin{document}
\begin{align}
\sum_i{ c_i}           &= \cos \sin\cos \sin\cos \sin\cos \sin\cos \sin \\
\sum_i{ c_i}           &= \delta \cos \sin\cos \sin\cos \cos \sin\cos \sin\cos \cos \sin\cos \sin\cos \cos \sin\cos \\ 
                       &\hphantom{{}=} \delta^2\sin\cos \cos \sin\cos \sin\cos \cos 
\end{align}
\end{document}

```

How do I align the last equation with the two above it? I have previously had success with `phantom`, but doesn't work here.

Answer: 
use `\mathrel{...}`

```
\documentclass[10pt, a4paper]{article}
\usepackage{amsfonts, amsmath, amssymb, amsfonts}
\begin{document}
\begin{align}
\sum_i{ c_i}           &= \cos \sin\cos \sin\cos \sin\cos \sin\cos \sin \\
\sum_i{ c_i}           &= \delta \cos \sin\cos \sin\cos \cos \sin\cos \sin\cos \cos \sin\cos \sin\cos \cos \sin\cos \\ 
                       &\mathrel{\hphantom{=}}\delta^2\sin\cos \cos \sin\cos \sin\cos \cos 
\end{align}
\end{document}

```
I typically use

```
\begin{align}
  ... = {} & ... \\
      = {} & ... \\
           & ...
\end{align}

```

note the set of `{}` between the `=` and the `&` a lot faster to type than `\phantom` and friends