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  • The coefficient of a^-6 b^4 in the expansion of (1/a –2b/3 )^10 is ______________

The coefficient of a^{-6}b^{4} in the expansion of \left ( \frac{1}{a}-\frac{2b}{3} \right )^{10} is ______________

Answers (1)

Given: (1/a – 2b/3)10

Thus, Tr+1 = 10Cr(1/a)10-r (-2b/3)r

Now, for the coefficient of a-6b4,

10 – r = 6

Thus, r = 4

Therefore the coefficient of a-6b4 = 10C4(-2/3)4

                                                              = 10.9.8.7.6!/6!.4.3.2.1  .  24/34

                                                              = 1120/27
 

Posted by

infoexpert22

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