I’ve got many of the following type of thing: a+2da + 2d

The first part of the span’s content is part of a math expression a+2d (without spaces) and the second part has the same text, but with spaces around the operator: a + 2d. I need to be able to capture the a+2d so I can remove it.

Some examples of the expressions I’ve got:
x-y=3x - y = 3, a+b-c=da + b - c = d, x-y=3x - y = 3 and it could involve underscores and brackets, like a_n=a+(n−1)da_n = a + (n - 1)d

I can find the first half (only) of the simpler examples using the regex:

/((\w*[\+|\-|\=]\w*)*)<\/span>/

and the second half (only) with spaces using

/((\w* [\+|\-|\=] \w*)*)<\/span>/

But I have no idea how to match the 2nd half given the first, or vice-versa. None of the look ahead or look behind examples I came across fit the situation, and became complicated very quickly.