[tex]keliling = 2r \: r = \pi \: d \\ luas \: = n{r}^{2} = \frac{1}{4} \pi {d}^{2} \\ tentukan \: \\ 1. \: keliling \:lingkran \: dan \: luas \\ a. \: r = 70cm

No. 1A

[tex]K = 2\pi r = 2 \cdot \frac{22}{7} \cdot 70\:\text{cm} = 440\:\text{cm} \\ \\ L = \pi r^2 = \frac{22}{7} \cdot 70\:\text{cm} \cdot 70\:\text{cm} = 15400\:\text{cm}^2 = 1.54\:\text{m}^2[/tex]

No. 1B

[tex]K = 2\pi r = 2 \cdot 3.14 \cdot 10\:\text{cm} = 62.8\:\text{cm} \\ \\ L = \pi r^2 = 3.14 \cdot 10\:\text{cm} \cdot 10\:\text{cm} = 314\:\text{cm}^2[/tex]

No. 1C

[tex]K = \pi d = \cdot \frac{22}{7} \cdot 21\:\text{cm} = 66\:\text{cm} \\ \\ L = \frac{1}{4} \pi d^2 = \frac{1}{4} \frac{22}{7} \cdot 21\:\text{cm} \cdot 21\:\text{cm} = 346.5\:\text{cm}^2[/tex]

No. 1D

[tex]K = \pi d = 3.14 \cdot 15\:\text{cm} = 47.1\:\text{cm} \\ \\ L = \frac{1}{4} \pi d^2 = \frac{1}{4} \cdot 3.14 \cdot 15\:\text{cm} \cdot 15\:\text{cm} = 176.625\:\text{cm}^2[/tex]

No. 2A

[tex]r = \frac{K}{2\pi} = \frac{66\:\text{cm}}{2\cdot(22/7)} = \frac{33\cdot7}{22}\:\text{cm} = 10.5\:\text{cm}[/tex]

No. 2B

[tex]r = \frac{K}{2\pi} = \frac{94.2\:\text{cm}}{2\cdot3.14} = \frac{30}{2}\:\text{cm} = 15\:\text{cm}[/tex]

No. 2C

[tex]r = \sqrt{\frac{L}{\pi}} = \sqrt{\frac{154\:\text{cm}^2}{22/7}}=\sqrt{49\:\text{cm}^2}=7\:\text{cm}[/tex]

No. 2D

[tex]r = \sqrt{\frac{L}{\pi}} = \sqrt{\frac{314\:\text{cm}^2}{3.14}}=\sqrt{100\:\text{cm}^2}=10\:\text{cm}[/tex]