Question

Panjang jari jari alas sebuah kerucut 5 cm, dan luas selimutnya 65 phi cm ^2. Volume kerucut tersebut adalah...?

Answer 1

L selimut kerucut = 65 phi
phi.r.s = 65 phi
phi.5.s = 65 phi
(kdua ruas phi tolong d coret sendiri)
5.s = 65
s = 65/5
s = 13 cm

maka :
t = √(s²-r²)
= √(13²-5²)
= √(169-25)
= √144
= 12 cm

jadi,
Volume kerucut
= 1/3.phi.r².t
= 1/3.3,14.5².12
= 4.3,14.25
= 3,14.100
= 314 cm kubik