5.5 The Substitution Rule/21

$\int {\frac {\cos {({\sqrt {t}})}}{\sqrt {t}}}\;dt$

${\begin{aligned}u&={\sqrt {t}}\\[2ex]du&={\frac {1}{2}}\ {\frac {1}{\sqrt {t}}}\;dt\\[2ex]2du&={\frac {1}{\sqrt {t}}}\;dt\end{aligned}}$

${\begin{aligned}\int {\frac {1}{\sqrt {t}}}\cos {({\sqrt {t}})}dt&=2\int \cos {u}\;du\\[2ex]&=2\sin {u}+c\\[2ex]&=2\sin({\sqrt {t}})+c\\[2ex]\end{aligned}}$