JAMB - Mathematics (1986 - No. 34)
Find the total surface area of solid cone of radius 2\(\sqrt{3}\)cm and slanting side 4\(\sqrt{3}\)
8\(\sqrt{3}\pi \)cm2
24\(\pi \)cm2
15\(\sqrt{3}\pi \)cm2
36\(\pi \)cm2
คำอธิบาย
Total surface area of a solid cone
r = 2\(\sqrt{3}\)
= \(\pi r^2\) + \(\pi\)rH
H = 4\(\sqrt{3}\), \(\pi\)r(r + H)
∴ Area = \(\pi\)2\(\sqrt{3}\) [2\(\sqrt{3}\) + 4\(\sqrt{3}\)]
= \(\pi\)2\(\sqrt{3}\)(6\(\sqrt{3}\))
= 12\(\pi\) x 3
= 36\(\pi \)cm2
r = 2\(\sqrt{3}\)
= \(\pi r^2\) + \(\pi\)rH
H = 4\(\sqrt{3}\), \(\pi\)r(r + H)
∴ Area = \(\pi\)2\(\sqrt{3}\) [2\(\sqrt{3}\) + 4\(\sqrt{3}\)]
= \(\pi\)2\(\sqrt{3}\)(6\(\sqrt{3}\))
= 12\(\pi\) x 3
= 36\(\pi \)cm2