Ques. 1JEE Main 2024, 30 January (Evening Shift)
Let = k=0n ( ( n Ck )2k+1 ) and = k=0n-1 ( n Ck n Ck+1k+2 ). If 5 =6 , then n equals .
Answer
10
Solution
∵ nCrr+1= n+1Cr+1n+1
= 1n+1 k=0nnCn-k n+1Ck+1= 2n+1Cn+1n+1
= 1n+1 k=0n-1nCn-k n+1Ck+2= 2n+1Cn+2n+1
∵ mCr nCs-r=m+nCs (lower indices add to n+1 and n+2)
= 2n+1Cn+22n+1Cn+1= nn+2
5 =6 nn+2= 56 n=10
Answer: 10