+118687 Find the coefficient of y^4 in the expansion of (2y - 5)^7.
The general term in the expansion will be
\(\binom{7}{n}(-5)^n(2y)^{7-n}\)
if I rearrange this I get
\(\binom{7}{n}(-5)^n(2)^{7-n}(y)^{7-n}\\ \)
you want y^4
so 7-n=4 gives n=3
sub n=3 into the term and you will have your answer
\(\binom{7}{n}(-5)^n(2)^{7-n}(y)^{7-n}\\ n=3\\ \binom{7}{3}(-5)^3(2)^{7-3}(y)^{7-3}\\ \)
You can finish it.
