lingkaran berdiameter 21cm luasnya=

[tex]l = \pi \times r \times r \\ l = \frac{22}{7} \times 10.5 \times 10.5 \\ l = 346.5 \: cm {}^{2} \\ [/tex]
r=21/2
=10,5 cm

Lingkaran berdiameter 21cm,
berjari jari 21/2cm
Luas = 22/7×21/2×21/2
Luas = 346,5cm2
Terima kasih ^_^