Question
Prove $\int_{-1}^{1} x^{17} \cos ^{4} \times d x=0$

Answer

Let $\mathrm{I}=\int_{-1}^{1} \mathrm{x}^{17} \cdot \cos ^{4} \mathrm{xdx}$
As we can see $f(x) =x^{17}.\cos^4x$ and $f(-x) = (-x)^{17}.\cos^4(-x) = -x^{17}.\cos^4x$
i.e. $f(x) = -f(-x)$
so, it is an odd function.
It is also known that if $f(x)$ is an odd function then $\left\{\int_{-a}^{a} f(x) d x=0\right\}$
$\Rightarrow \mathrm{I}=\int_{-1}^{1} \mathrm{x}^{17} \cdot \cos ^{4} \mathrm{xdx}=0$
Hence proved.

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