perhatikan gambar L alas belahan tabung → 9π cm² tinggi tabung → 12 cm

9pi x 4 = 36pi cm^2 --- luas alas total jika bulat

Pi r^2 = 36 pi
r^2 = 36
r = 6 cm --- jari jari (a)

6 x 12 = 72 cm^2 --- arsiran (b)