\[ \int \sqrt {a \cos ^3(x)} \, dx \]
Optimal antiderivative \[ \frac {2 \sqrt {\frac {\cos \left (x \right )}{2}+\frac {1}{2}}\, \EllipticF \left (\sin \left (\frac {x}{2}\right ), \sqrt {2}\right ) \sqrt {a \left (\cos ^{3}\left (x \right )\right )}}{3 \cos \left (\frac {x}{2}\right ) \cos \left (x \right )^{\frac {3}{2}}}+\frac {2 \sqrt {a \left (\cos ^{3}\left (x \right )\right )}\, \tan \left (x \right )}{3} \]
command
integrate((a*cos(x)^3)^(1/2),x, algorithm="fricas")
Fricas 1.3.8 (sbcl 2.2.11.debian) via sagemath 9.6 output
\[ \frac {i \, \sqrt {2} \sqrt {a} \cos \left (x\right ) {\rm weierstrassPInverse}\left (-4, 0, \cos \left (x\right ) + i \, \sin \left (x\right )\right ) - i \, \sqrt {2} \sqrt {a} \cos \left (x\right ) {\rm weierstrassPInverse}\left (-4, 0, \cos \left (x\right ) - i \, \sin \left (x\right )\right ) + 2 \, \sqrt {a \cos \left (x\right )^{3}} \sin \left (x\right )}{3 \, \cos \left (x\right )} \]
Fricas 1.3.7 via sagemath 9.3 output
\[ {\rm integral}\left (\sqrt {a \cos \left (x\right )^{3}}, x\right ) \]