Browse Questions

# If the $r^{th}$ term in the expansion of $(\large\frac{x}{3}-\frac{2}{x^2})^{10}$ contains $x^4$ then $r$ is equal to

$\begin{array}{1 1}(A)\;4\\(B)\;3\\(C)\;2\\(D)\;\text{none of these}\end{array}$

Can you answer this question?

Toolbox:
• $T_{r+1}=nC_ra^{n-r} b^r$
$T_r=T_{(r-1)}+1=10C_{r-1}(\large\frac{x}{3})^{10-(r-1)}(-\large\frac{2}{x^2})^{r-1}$