JEE Main 2021MathematicsBinomial TheoremEasyMCQ

JEE Main 2021 — Binomial Theorem Question with Solution

JEE Main 2021 (27 Jul Shift 1)

Question

If the coefficients of x7 in x2+1bx11 and x-7 in x-1bx211,b≠0, are equal, then the value of b is equal to:

Choose an option

Show full solutionCorrect option: C
Correct answer
C1

Step-by-step explanation

Coefficient of x7 in x2+1bx11

=Cr11x211-r·1bxr

=Cr11x22-3r·1 br

So, 22-3r=7

⇒r=5

So, the term is C511·1 b5·x7

Coefficient of x-7 in x-1bx211

=Cr11x11-r·-1 bx2r

=Cr11x11-3r·-1rbr

So, 11-3r=-7   ∴ r=6

So, the term is C611·1 b6x-7

Hence, C511·1 b5=C611·1 b6

Since b≠0 ∴ b=1

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About this question

This is a previous-year question from JEE Main 2021, 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.