JEE Main 2015MathematicsBinomial TheoremMediumMCQ

JEE Main 2015 — Binomial Theorem Question with Solution

JEE Main 2015 (10 Apr Online)

Question

If the coefficient of the three successive terms in the binomial expansion of 1+xn are in the ratio 1:7:42, then the first of these terms in the expansion is

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Show full solutionCorrect option: D
Correct answer
D7th

Step-by-step explanation

Let coefficient of first term is Crn 

CrnCr+1n=17

⇒ r+1n-r=17

⇒ 7r+7=n-r

n-8r=7       …1 

Also,  Cr+1nCr+2n=742=16

⇒r+2n-r-1=16

⇒6r+12=n-r-1

n-7r=13       …2 

Solving 1 and 2, we get r=6

Hence, 7th term is the answer. 

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About this question

This is a previous-year question from JEE Main 2015, covering the Binomial Theorem chapter of Mathematics. PrepSharp catalogues every PYQ from JEE Main with a verified answer key and step-by-step solution prepared by IIT alumni — so you can search by chapter, topic or year and revise efficiently.