```
\usepackage{mathtools, amssymb, amsthm}
\begin{align}\label{eq1}
\sum_{n}\lambda^{n}(i)-\sum_{n}\lambda^{n}(j) \nonumber\\=\begin{cases}
\lambda_{n}, &\text{if } n = i\\
-\lambda_{n}, &\text{if } n = i\\
0, &\text{otherwise}
\end{cases}
\text{ }\forall i, j
\end{align}
```

First line of the equation must be left aligned (or at least adjustable, `\hspace`

not working). `\sum_{n}\lambda^{n}(i)-\sum_{n}\lambda^{n}(j) \nonumber`

then according to first line `cases`

will be aligned. However, equation number should be at extreme right.

As per clarification request by @Mico The first pic from the answer.

What I need is the following pic:

The alignment of the starting of the equation is preferably left (or adjustable)

## Best Answer

I'm not sure what the proposed alignment should achieve, but here it is: