hitunglah keliling lingkaran, jika panjang jari jarinya: 21 cm

Diameter
= 21 x 2
= 42 cm

Keliling
= phi x d
= 22/7 x 42
= 132 cm

k = 2×phi×r
= 2×22/7×21
= 2×22×3
= 44×3
= 132cm