Diketahui:

Kerucut:

Volume = 12.936 cm³ dan tinggi $t$ = 28 cm.

Ditanya:

Luas selimut kerucut = $L_s$ =?

Dijawab:

Perhatikan gambar kerucut di bawah ini.

Volume kerucut:

$V=\frac{1}{3}\pi r^2t$

$\leftrightarrow12.936=\frac{1}{3}\times\frac{22}{7}\times r^2\times28$

$\leftrightarrow12.936=\frac{1}{3}\times22\times r^2\times4$

$\leftrightarrow12.936\ \times3=22\times r^2\times4$

$\leftrightarrow38.808=88\times r^2$

$\leftrightarrow r^2=\frac{38.808}{88}$

$\leftrightarrow r^2=441$

$\leftrightarrow r^2=21^2$

$\leftrightarrow r=21$ cm.

Garis lukis kerucut:

$s^2=r^2+t^2$

$\leftrightarrow s^2=21^2+28^2$

$\leftrightarrow s^2=441+784$

$\leftrightarrow s^2=1.225$

$\leftrightarrow s^2=35^2$

$\leftrightarrow s=35$ cm.

Luas selimut kerucut:

$L_s=\pi rs$

$\leftrightarrow L_s=\frac{22}{7}\times21\times35$

$\leftrightarrow L_s=22\times21\times5$

$\leftrightarrow L_s=2.310$ cm².

Jadi, luas selimut kerucut 2.310 cm².