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The coefficient of a–6b4 in the expansion of (1a-2b3)10 is ______.

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Question

The coefficient of a–6b4 in the expansion of `(1/a - (2b)/3)^10` is ______.

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Solution

The coefficient of a–6b4 in the expansion of `(1/a - (2b)/3)^10` is `1120/27`.

Explanation:

The given expansion is `(1/a - (2b)/3)^10`

From a–6b4 

We can take r = 4

∴ T5 = T4+1

= `""^10"C"_4 (1/a)^(10 - 4) (- (2b)/3)^4`

= `""^10"C"_4 (1/a)^6 ((-2)/3)^4 * b^4`

= `(10*9*8*7)/(4*3*2*1) xx 16/81 * a^-6b^4`

= `210 xx 16/81 a^-6b^4`

= `1120/27 a^-6b^4`

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Chapter 8: Binomial Theorem - Exercise [Page 146]

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NCERT Exemplar Mathematics [English] Class 11
Chapter 8 Binomial Theorem
Exercise | Q 29 | Page 146

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