R=21cm Luas lingkaran=

22/7.21.21=1386
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[tex]luas \: lingkaran = \pi \times {r}^{2} \\ = \frac{22}{7} \times 21 \times 21 \\ = \frac{22}{7} \times 441 \\ = 9.702 \div 7 \\ =1.386[/tex]
Semoga membantuu