Question
Question: Given the integers r\>1, n\> 2, and co-efficients of (3r) <sup>th</sup> and (r+2)<sup>th</sup> term...
Given the integers r>1, n> 2, and co-efficients of (3r) th and
(r+2)th term in the binomial expansion of (1+x)2n are equal, then
A
n = 2r
B
n =3r
C
n = 2r+1
D
None of these
Answer
None of these
Explanation
Solution
Coefficients of (3r)th and (r + 2)th terms will be 2nC3r−1 and 2nCr+1.
These are equal
⇒ (3r − 1) + (r + 1) = 2n⇒ n = 2r