Question

If $\underset{0}{\overset{1}{\int }}\left(x^{21}+x^{14}+x^7\right){\left(2x^{14}+3x^7+6\right)}^{1/7}dx=\frac{1}{l}(11{)}^{m/n}$ where $l,m,n\in N,m$ and $n$ are coprime then $l+m+n$ is equal to ______

Answer 1

Answer: 63

$\int \left(x^{20}+x^{13}+x^6\right){\left(2x^{21}+3x^{14}+6x^7\right)}^{1/7}dx$
$2x^{21}+3x^{14}+6x^7=t$
$42\left(x^{20}+x^{13}+x^6\right)dx=dt$
$\frac{1}{42}\underset{0}{\overset{11}{\int }}{t}^{\frac{1}{7}}dt={\left(\frac{t^{\frac{8}{7}}}{\frac{8}{7}}\times \frac{1}{42}\right)}_0^{11}$
$=\frac{1}{48}{\left(t^{\frac{8}{7}}\right)}_0^{11}=\frac{1}{48}(11{)}^{8/7}$
$l=48,m=8,n=7$
$l+m+n=63$