Question

find the term that contains x^8 y^9 in the expansion of (x^2+3y^3)^7

Answer 1

2 times what is eight?

Answer 2

\[\binom{7}{n-1}(x^2)^{n}~(3y^3)^{7-n}\]

Answer 3

the n-1 might be a bad memory tho

Answer 4

\[(a+b)^n=\sum_{k=0}^n\binom{n}{k}a^{n-k}b^{k}\]
thats better