Jawaban:

1. r = 70

d = 2 × r

= 2 × 70 cm

= 140 cm

luas = phi × r × r

= 22/7 × 70 cm × 70 cm

= 22/7 × 4.900 cm²

= 15.400 cm²

keliling = phi × d

= 22/7 × 140 cm

= 440 cm

2. r = 49 cm

d = 2 × r

= 2 × 49 cm

= 98 cm

luas = phi × r × r

= 22/7 × 49 cm × 49 cm

= 22/7 × 2.401 cm²

= 7.546 cm²

keliling = phi × d

= 22/7 × 98 cm

= 308

3. r = 42 cm

d = 2 × r

= 2 × 42 cm

= 84 cm

luas = phi × r × r

= 22/7 × 42 cm × 42 cm

= 22/7 × 1.764 cm²

= 5.544 cm ²

keliling = phi × d

= 22/7 × 84 cm

= 264

4. d = 40 cm

r = d ÷ 2

= 40 cm ÷ 2

= 20 cm

luas = phi × r × r

= 3,14 × 20 cm × 20 cm

= 3,14 × 400 cm²

= 1.256

keliling = phi × d

= 3,14 × 40 cm

= 125,6

5. d = 12

r = d ÷ 2

= 12 cm ÷ 2

= 6 cm

luas = phi × r × r

= 3,14 × 6 cm × 6 cm

= 3,14 × 36 cm²

= 113,04

keliling = phi × d

= 3,14 × 12 cm

= 37,68

Note :

phi ada 2 yaitu :

- 22/7 : hanya digunakan jika d / r nya adalah kelipatan 7

- 3,14 : hanya digunakan jika d / r nya bukan kelipatan 7