JEE MainMathematicsBinomial TheoremMCQ+4 / −1
If the constant term in the expansion of is 2k.l, where l is an odd integer, then the value of k is equal to:
- A6
- B7
- C8
- D9
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Correct answer: D
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We need the constant term in
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In the general term of the multinomial expansion, if we choose:
- times the term ,
- times the term ,
- times the term ,
then and the corresponding term is
- For this term to be constant, the power of must be zero:
So we solve
- Substitute into the second equation:
Now find non-negative integer solutions.
Testing values of :
- If , then . Then
This gives the valid solution
No other non-negative integer solution works.
- Therefore the constant term is
Now compute:
Hence constant term
First, So
- We are told this constant term is of the form , where is odd.
Now factorize: Also, So, where is odd.
Thus,
- Therefore the correct option is
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