Question

In Mathematica if I have a symbolic algebra equation, how can I get the factor which is multiplied by a specific term?

I mean, say, as the result of some calculation I get a symbolic equation a x^2 + b x + c y, and say I am interested in whatever is multiplied by x^2 (i.e. a in here). What statement should I write such that if applied to a x^2 + b x + c y returns a.

(note that in the example there is a b x term so I cannot use derivatives to extract the factor)

Answer 1

I believe what you are asking for is how to extract a coefficient. For polynomial expressions you can use something like this:

In[1]:=  Coefficient[(x+y)^3, xy^2]
Out[1]:= 3

More generally, if you want to get all the coefficients, you can use CoefficientList like so:

In[1]:= f = a x^2 + b x + c;
CoefficientList[f, x]

Out[2]= {c, b, a}