Show that the height of the cone of maximum volume that can be inscribed in a sphere of radius 12 cm is 16 cm.
Let a cone of radius r cm and height h cm is inscribed in a sphere of radius 12 cm.
In right triangle AOB,
(12)2 = (h – 12)2 + r2
r2 =24h – h2
Now, V = (1/3)πr2h
V = (1/3)π(24h – h2)h (Substituting the value of r2)
V = (1/3) π(24h2 – h3)
dV/dh = (1/3) π (48h – 3h2)
For maximum volume: dV/dh = 0
Therefore, we get
(1/3) π (48h – 3h2) = 0
48h – 3h2 = 0
h = 16.
Also, d2V/dh2 = 1/3 π (48 – 6h)
(d2V/dh2 )h = 16 = 1/3 π (48 – 96) < 0.
Therefore, for h = 16, volume is maximum.
Hence, height of the cone of maximum volume, which can be inscribed in a sphere of radius 12 cm is 16 cm.