Question

What is the approximate surface area of the larger cone?
A.467.5
B.267.1
C.152.7
D.817.8

Answer 1

both cones are similar right ?

Answer 2

yes

Answer 3

since the surface are of a cone is equal to its base area, plus its lateral area ....

pi r^2 + .... i can never remember the lateral area without a picture

Answer 4

\[arc=\theta~r\]
\[area=\frac{\theta}{2}~r^2\]

Answer 5

surface area = \(\pi r^2 + \pi r l\)

\(r\) : radius
\(l\) : slant height

Answer 6

yeah, that one :)

Answer 7

:) may be we can first find surface area of small cone

Answer 8

then multiply it with (sf)^2

Answer 9

sf = scale factor

Answer 10

no need, just relate the triangles

Answer 11

ok thx i was just wondering if i set up a proportion

Answer 12

yea its simple this way :)

Answer 13

proportion :-

\(\large \frac{21}{12} = \frac{R}{5}\)


solve R

Answer 14

R is 8.75

Answer 15

Yes, R = 8.75

Answer 16

and slant height \(l\) = 21

Answer 17

plug them in the formula

Answer 18

ok thx i got it from here

Answer 19

sounds good :)