Tolong dibantu dgn caranya :)

[tex]d {}^{2} = 20 {}^{2} - 16 {}^{2} \\ d {}^{2} = 400 - 256 \\ d {}^{2} = 144 \\ d = \sqrt144 \\ d = 12 \: cm \\ \\ luas = \frac{1}{2} \times \pi \: r {}^{2} \\ luas = \pi \: \times 3 \times 6 \\ luas \: = 18\pi[/tex]