Question
Evaluate : $\int_0^1 x(1-x)^n d x$; $($ where $n \in N)$

Answer

$\int_0^1 x(1-x)^n d x$
$\begin{array}{c}=\int_0^1(1-x)\{1-(1-x)\}^n d x,\left(a s, \int_0^a f(x) d x=\int_0^a f(a-x) d x\right) \\ =\int_0^1 x^n(1-x) d x \\ =\int_0^1 x^n d x-\int_0^1 x^{n+1} d x \\ =\frac{1}{n+1}\left[x^{n+1}\right]_0^1-\frac{1}{n+2}\left[x^{n+2}\right]_0^1 \\ =\frac{1}{n+1}-\frac{1}{n+2}=\frac{1}{(n+1)(n+2)}\end{array}$

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