[tex]f(t)=-20\cos\left(\frac{\pi}{5}t\right)+50\\f'(t)=20\sin(\frac{\pi}{5}t)*(\frac{\pi}{5})=0\\\sin(\frac{\pi}{5}t)=0\\\frac{\pi}{5}t=0,\pi\\t=0,5\\\\f(0)=-20\cos(\frac{\pi}{5}(0))+50\\f(0)=-20+50\\f(0)=30\\f(5)=-20\cos(\frac{\pi}{5}(5))+50\\f(5)=-20(-1)+50\\f(5)=20+50\\f(5)=70[/tex]
f(t) = -20 * cos(pi / 5) + 50