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Friday, 4 December 2015

Find a formula for the $n$-th derivative of $f(x) = \displaystyle {e^x\over 1 - x}$.

Question
Find a formula for the $n$-th derivative of  $f(x) = \displaystyle {e^x\over 1 - x}$. That is find a formula for $f^{(n)}(x)$. Also write out the derivative for $n = 1, 2, 3$.

A formula that is used here for the $n$-th derivative of a function that is a product of two other functions, $f(x)=u(x).v(x)$ was proven in ANOTHER POST (CLICK ME). The result is that


$${d^n \over dx^n } (uv)=\sum^n_{r=0} {n\choose r} u^{(r)}v^{(n-r)}$$
This formula is used to write down the $n$-th derivative of 

$f(x) = \displaystyle{e^x\over 1 - x}$


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