Jawaban:

a. r = 5 m

D = 10 m

b. r = 6 cm

D = 12 cm

c. r = 12 m

D = 24 m

d. r = 10 dm

D = 20 dm

e. r = 42 cm

D = 84 cm

Penjelasan dengan langkah-langkah:

Rumus Luas Lingkaran = π x r x r

a. L = π x r x r

78.5 = 3.14 x r²

78.5 x 100 : 314 = r²

25 = r²

√25 = r

5 = r

jari - jari = 5 m

Diameter = 2 x jari-jari

Diameter = 2 x 5 = 10 m

b. L = π x r x r

792/7 = 22/7 x r²

792/7 x 7/22 = r²

792/22 = r²

36 = r²

√36 = r

6 = r

jari - jari = 6 cm

Diameter = 2 x jari-jari

Diameter = 2 x 6 = 12 cm

c. L = π x r x r

452.16 = 3.14 x r²

452.16 x 100 : 314 = r²

144 = r²

√144 = r

12 = r

Jari - Jari = 12 m

Diameter = 2 x jari-jari

Diameter = 2 x 12 = 24 m

d. L = π x r x r

2200/7 = 22/7 x r²

2200/7 x 7/22 = r²

2200/22 = r²

100 = r²

√100 = r

10 = r

Jari Jari = 10 dm

Diameter = 2 x jari-jari

Diameter = 2 x 10 = 20 dm

e. L = π x r x r

5544 = 22/7 x r²

5544 x 7/22 = r²

1764 = r²

√1764 = r

42 = r

Jari Jari = 42 cm

Diameter = 2 x jari-jari

Diameter = 2 x 42 = 84 cm