Помогите пж задания 5,6,7,8, (б и в) все 8 задач

Некоторые ответы округлены.

5. $C = 2\*pi*r$
б) $C=2*\pi*\frac{6}{\pi}= \frac{2\pi6}{\pi} =2*6=12$
в) $C=2*\pi*0,(4)=2*3,14*\frac{4}{9}= \frac{2*3,14*4}{9}=\frac{25,12}{9}=2,79(1)$

6. $C = \pi*d$
б) $C=6 \frac{2}{5}*3,14= \frac{32*3,14}{5} = 20$
в) $C=2,2(6)*3,14=7,117(3)$

7. $S=\pi*r^{2}$
б) $S= (\frac{3}{4})^{2} *3,14= \frac{9*3,14}{16}= \frac{28,26}{16}=1,76625$
в) $S=3,14*2,(3)=7,32(6)$

8. $S=\frac{\pi}{4}*d^{2}$
б) $S=0,785*(1 \frac{2}{5})^{2}=\frac{0,785*49}{25}= \frac{38,465}{25}=1,5386$
в) $S= \frac{\pi}{4}*( \frac{10}{\pi})^{2} = \frac{\pi*100}{4*\pi^{2}}= \frac{25}{\pi} = \frac{25}{3,14}= 8$