The coefficient of {x^{ - 7}} in the expansio | vedclass

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Question

(b) For number of term, $(11 - r)(1) + r( - 2) = - 7$

$\Rightarrow 11 - r - 2r = - 7$

$ \Rightarrow r = 6$

Thus coefficient of $x^{-7}$ is $^

Vedclass · Accepted Answer

$\frac{{462{a^5}}}{{{b^6}}}$

Vedclass · Answer

(b) For number of term, $(11 - r)(1) + r( - 2) = - 7$

$\Rightarrow 11 - r - 2r = - 7$

$ \Rightarrow r = 6$

Thus coefficient of $x^{-7}$ is $^{11}{C_6}{(a)^5}{\left( { - \frac{1}{b}} \right)^6} $

$= \frac{{462}}{{{b^6}}}{a^5}$

The coefficient of ${x^{ - 7}}$ in the expansion of ${\left( {ax - \frac{1}{{b{x^2}}}} \right)^{11}}$ will be

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