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Binomial Theorem

Question
CBSEENMA11015667

The coefficient of the middle term in the binomial expansion in powers of x of (1 +αx)4  and of (1−αx )6  is the same if α equals

  • -5/3

  • 3/5

  • -3/10

  • 10/3

Solution

C.

-3/10

The coefficient of x in the middle term of expansion of (1+ αx)4= 4C22
The coefficient of x in middle term of the expansion of 3(1− αx) = 6C3 (−α)3
According to question
straight C presuperscript 4 subscript 2 straight alpha squared space equals space to the power of 6 straight C subscript 3 space left parenthesis negative straight alpha right parenthesis cubed
fraction numerator 4 factorial over denominator 2 factorial 2 factorial end fraction straight alpha squared space equals space minus space fraction numerator 6 factorial over denominator 3 factorial 3 factorial end fraction straight alpha cubed
6 straight alpha squared space equals space minus space 20 straight alpha cubed
straight alpha space equals space minus space 6 over 20
straight alpha space equals space minus 3 over 10

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