Answer
$8$
Work Step by Step
Use u-substitution to integrate the function
$\int_0^8 (\frac{2x}{\sqrt {x^2 +36}}) dx$, let $u=x^2+36$
$\int_0^8 u^{-\frac{1}{2}} du$
$[2u^{\frac{1}{2}}]_0^8$
$[2\sqrt {x^2 +36} ]_0^8$
$(2\sqrt {100} - 2\sqrt {36})$
$20-12= 8$
