# Thread: Binomial coefficients in expansions

1. ## Binomial coefficients in expansions

Hey guys,
Im having trouble with this problem, i dont want a solution just really need some help understanding how to go about looking at this problem and how to start it off.

Find the coefficient of x^3y^7 in the expansion of (3x-2y)^10

Thanks

2. Knowing that $\displaystyle \left( {a + b} \right)^n = \sum\limits_{k = 0}^n {{n \choose k} a^k b^{n - k} }$ surely you can answer your one question.

3. i see, how does the (3x -2y) influence the problem opposed to if u just had (x-y)?

thanks for the help

4. Originally Posted by fenix
i see, how does the (3x -2y) influence the problem opposed to if u just had (x-y)?

thanks for the help
a = 3x, b = (-2y), n = 10.

Now start by getting the general term as suggested by Plato.

5. I see thanks a lot for the help