if f(x)
Question:

If $f(x)=\int \frac{5 x^{8}+7 x^{6}}{\left(x^{2}+1+2 x^{7}\right)^{2}} d x,(x \geq 0), f(0)=0 \mathrm{v}$ and $f(1)=\frac{1}{\mathrm{~K}}$, then the value of $\mathrm{K}$ is

Solution:

$f(x)=\int \frac{\left(5 x^{8}+7 x^{6}\right) d x}{x^{14}\left(x^{-5}+x^{-7}+2\right)^{2}}$

Let $x^{-5}+x^{-7}+2=t$

$\left(-5 x^{-6}-7 x^{-8}\right) d x=d t$

$\Rightarrow f(x)=\int-\frac{d t}{t^{2}}=\frac{1}{t}+c$

$f(x)=\frac{x^{7}}{x^{2}+1+2 x^{7}}$

$f(1)=\frac{1}{4}$

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