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The coefficient of t^4 in ((1-t^6)/(1-t)...

The coefficient of `t^4` in `((1-t^6)/(1-t))^3` (a) `18` (b) `12` (c) `9` (d) `15`

Text Solution

Verified by Experts

The correct Answer is:
5

`((1-t^(6))/(1-t))=(1-t^(6))^(3)(1-t)^(-3)=(1-3C_(1)t^(6)+……..)(sum_(r=0)^(oo).^(3+r-1)C_(r)x^(r ))`
Coefficient of `x^(4)=.^(3+4-1)C_(4)=.^(6)C_(4)=15`
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