Q.use the binomial theorem to find the coefficient of x^5y^3 in (x-2y)^8.

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- Aug 9th 2006, 03:56 AMkodirlDiscrete maths
Q.use the binomial theorem to find the coefficient of x^5y^3 in (x-2y)^8.

- Aug 9th 2006, 04:31 AMCaptainBlackQuote:

Originally Posted by**kodirl**

$\displaystyle

(x-2y)^8=\sum_{r=0}^8 {8 \choose r}x^{n-r}(-2y)^{r}

$

So the coefficient of $\displaystyle x^5y^3$ is:

$\displaystyle

{8 \choose 3}(-2)^3=-\frac{8!\times 8}{5!\ 3!}

$

RonL