Question

What is the coefficient of the term x7y in the expansion of (x + y)8?
a.1
b.8
c.28
d.56

Answer 1

\[T _{r+1}=C_{r}{8}x ^{8-r}y ^{r}\]
put r=1\[T _{9}=C _{1}^{8}x^7y^1=\frac{ 8 }{ 1 }x^7y=8x^7y\]
coefficient of x^7y=?