carilah keliling lingkaran jika diketahui diameternya 28 cm

jari-jari = ½ diameter
jari - jari = ½ . 28
jari - jari = 14
keliling = 2πr = 2 . 22/7 . 14 = 88 cm

d=28cm, r=14cm

keliling lingkaran = 2πr
=2 . 22/7 .14
=2 .44
=88cm