I have an equation which I rearrange in several steps. I want to show this, by having a single numbered equation, which has an aligned equal sign on the right, and the terms left of the equal sign are centered in each line. So basically it looks like this:
(a+b)^3 = (a+b)(a+b)^2 = (a+b)(a+b)(a+b) = (1) (a^2+2ab+b^2)(a+b) = (a^3+3a^2b+3ab^2+b^3) =
I know about aligned, gather and split, but neither seems to achieve, what I want.
Update: This is no duplicate to the linked question, as I want a fixed sign on the right, and a horizontal centered alignement on the left. The linked question has no horizontal centering in it.