# Math Help - it lost me

1. ## it lost me

What is the coefficients of x^8 y^9 in the expansion of (3x + 2y)^17?

2. Originally Posted by lkrb
What is the coefficients of x^8 y^9 in the expansion of (3x + 2y)^17?
Just use the binomial theorem.

3. Originally Posted by lkrb
What is the coefficients of x^8 y^9 in the expansion of (3x + 2y)^17?
Originally Posted by janvdl
Just use the binomial theorem.
correct. to be more specific. the formula for binomial expansion is:

$(a + b)^n = \sum_{k = 0}^{n} {n \choose k}a^k b^{n - k}$

though i much prefer it in the order (it's exactly the same thing) of $\sum_{k = 0}^{n} {n \choose k}a^{n - k}b^k$

Here you have $a = 3x$ and $b = 2y$, and you want the term given by $k = 9$ (using the second formula)

4. Just like guys here mentioned... you use binomial theorem. So your final answer would be [17! / (8! * 9!)] * (3^8) (2^9).