How to align a set of my equations?

Question

I just wan't to align the equation like this example (Of course, I can't align these equations on the web page):

∵△ABC ≌ △A′B′C′
∴∠ABC = ∠A′B′C′
  ∠ACB = ∠A′C′B′
  ∠BAC = ∠B′A′C′

If I use &, these will be to much spaces...

Answer 1

Update:

You can use a space \, or use alignat as told by Gonzalo Medina

\documentclass{article}
\usepackage{mathtools} %% provides amsmath with additional features and bug fixes
\usepackage{amssymb}   %% provides symbols like \because and \therefore

\begin{document}
Using \verb|align|

\begin{align*}
    \because \triangle \mathrm{ABC}   &= \triangle \mathrm{A^{'}B^{'}C^{'}}   \\
    \therefore\, \angle \mathrm{ABC}  &= \angle  \mathrm{A^{'}B^{'}C^{'}}     \\
    \angle \mathrm{ACB}               &= \angle \mathrm{A^{'}C^{'}B^{'}}      \\
    \angle \mathrm{BAC}               &= \angle \mathrm{B^{'}A^{'}C^{'} }
\end{align*}

Using \verb|alignat|
\begin{alignat*}{3}
&\because   &\triangle \mathrm{ABC} &= \triangle \mathrm{A^{'}B^{'}C^{'}}   \\
&\therefore &\angle \mathrm{ABC}    &= \angle \mathrm{A^{'}B^{'}C^{'}}      \\
&           &\angle \mathrm{ACB}    &= \angle \mathrm{A^{'}C^{'}B^{'}}      \\
&           &\angle \mathrm{BAC}    &= \angle \mathrm{B^{'}A^{'}C^{'} }
\end{alignat*}

\end{document}