Answer:
-540
Step-by-step explanation:
The coefficient of the k-th term of (a+b)^n is nCk. (k = 0, 1, 2, ..., n)
Here, we want the coefficient of a^3b^3 for n=6, so k=3 and the coefficient is ...
6C3 = 6!/(3!(6-3)!) = 5·4 = 20
So for a=3x and b=-y, we want ...
20a^3b^3 = 20(3x)^3(-y)^3 = -540x^3y^2
The coefficient you're looking for is -540.
