7.1 Integration By Parts/30

$\int _{0}^{1}{\frac {r^{3}}{\sqrt {4+r^{2}}}}\cdot dr$

Failed to parse (unknown function "\cdotdr"): {\displaystyle \begin{align} u &= 4+r^{2} \\[2ex] r^{2} &= u-4 \\[2ex] 2r\cdotdr&= du; \\[2ex] du &= \frac{1}{\sqrt{1-x^2}}\;dx \\[2ex] \end{align} }

$\int _{0}^{1}{\frac {r^{3}}{\sqrt {4+r^{2}}}}\cdot dr~~~=~~~\int _{0}^{1}r^{3}\cdot {\frac {1}{\sqrt {4+r^{2}}}}\cdot dr$