Jawaban:

8. keliling= π × d

= 22/7 × 7

= 22cm

9. keliling= 2 × π × r

= 2 × 22/7 × 21

= 2 × 66

= 132cm

10. L= π × r²

= 22/7 × 70²

= 22/7 × 4900

= 15400 cm²

11. L= π × r²

= 3,14 × 30²

= 3,14 × 900

= 2.826 cm²

12. r = d/2

r = 42/2

r = 21 cm

Luas permukaan roda

= π x r x r

= 22/7 x 21 x 21

= 22 x 3 x 21

= 1.386 cm²

13. Diketahui:

Keliling lingkaran = 314 cm

π = 3,14

Ditanya:

Luas = ... ?

Jawab:

Kita cari jari-jari terlebih dahulu

Keliling lingkaran = 2 x π x r

314 = 2 x 3,14 x r

314 = 6,28 x r

r = 314 : 6,28

r = 50

Langkah selanjutnya kita cari luasnya

Luas lingkaran = π x r²

= 3,14 x 50 x 50

= 3,14 x 2500

= 7.850 cm²

14. L = πr² k = 2πr

1.256 = 3,14 × r²

1.256/3,14 = r²

400 = r²

r = √400 = 20 cm

jadi...,

k = 2πr

k = 2 × 3,14 × 20

k = 125,6 cm

15. Luas= 1/2 × π × r²

= 1/2 × 22/7 × 28²

= 1/2 × 2.464

= 1.232 m²

keliling= π × r

= 22/7 × 28

= 88 m

Jadikan jawaban yang terbaik ya!!