Ask Questions, Get Answers

Want to ask us a question? Click here
Browse Questions
Home  >>  CBSE XI  >>  Math  >>  Binomial Theorem
0 votes

If there is a term containing $x^{2r}$ in $(x+\large\frac{1}{x^2})^{n-3}$ then

$\begin{array}{1 1}(A)\;\text{n-2r is a positive integral multiple of 3}\\(B)\;\text{n-2r is even}\\(C)\;\text{n-2r is odd}\\(D)\;\text{none of these}\end{array} $

Can you answer this question?

1 Answer

0 votes
  • $T_{r+1}=nC_r a^{n-r} b^r$
$T_{k+1}$ in $(x+\large\frac{1}{x^2})^{n-3}$
$\Rightarrow n-3 C_k x^{n-3-k} (\large\frac{1}{x^2})^k$
$\Rightarrow n-3 C_k x^{n-3-3k}$
Let $T_{r+1}$ contains $x^{2r}$
$\therefore n-3-3^k=2r$
$\therefore n-2r$ is a positive integral multiple of 3
Hence (A) is the correct answer.
answered Jun 25, 2014 by sreemathi.v

Related questions

Ask Question
student study plans
JEE MAIN, CBSE, NEET Mobile and Tablet App
The ultimate mobile app to help you crack your examinations
Get the Android App