# Pick up certain terms in multiplication [closed]

Suppose I have the following expression:

(2a + 3b)^2

when expanded, it gives

4a^2 + 9b^2 +6a*b

I want to pick up only the terms involving a* b, that is the term 6a*b. Is there an automatic way to pick up this kind of terms? (of course in the above example it is very simple, but I want it to work automatically for more complicated cases.)

• Check your expansion. Aug 24 at 16:49
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• It would be helpful if you were to show some of the more complicated cases Aug 25 at 15:58

Coefficient[(2 a + 3 b)^2, a b] a b