Hallo!

(-(4r/3pi)-r)*(pi/2)*r^2

\(\large (-\frac{4r}{3\pi}-r)\times\frac{\pi}{2}r^2\)

\(\large =-\frac{4\pi r^3}{3\pi}-\frac{\pi r^3}{2}\)

\(\large=\frac{8r^3-3\pi r^3}{6}\)

\(\large=r^3(\frac{8-3\pi}{6})\)

\(\large=-1,0471975512 \ r^3\)

   !

OR

\(((\frac{-4r}{3}\pi)-r)*(\frac{\pi}{2}*r^2)\\ =(\frac{-4r\pi-3r}{3})*(\frac{\pi r^2}{2})\\ =\frac{1}{6}(-4\pi r-3r)(\pi r^2)\\ =\frac{\pi r^3}{6}(-4\pi -3)\\ =\frac{-\pi r^3}{6}(4\pi +3)\\ \)