In school, our teacher requires us to put a ⇔ sign on the left of our equations, when we do a tranformation on the equation. Usually, I use an
align context to format multiple transformations of an equation, but I don't know, how to add that extra sign on the left. In the best case, want them to be all align on the same line, like in this image:
Now, how can I do this in (La)TeX?