Question

Multiple choice: Can someone please please help me with some more surface area of pyramids and cones???

Answer 1

do you know the formula for finding out the surface area of a cone?

Answer 2

if not, it is \[\pi (radius)^{2} + (\pi *radius* hypotenuse)\]

In the given figure, the radius is denoted by r and the height of the cone is denoted by y. so, by pythogarus's theorem, the hypotenuse, denoted by x is \[\sqrt{r ^{2}+y ^{2}}\]

Answer 3

all you need to do now is substitute the values of the radius and hypotenuse in the formula and you will have your answer

Answer 4

i think its c, but i want a second opinion

Answer 5

how did you get c?

Answer 6

i did it but i lost the paper

Answer 7

so, 138.23m^2 is the surface area.
substituting in the formula, we get,
\[138.23 = \pi*2^{2}+\pi*2*\sqrt{2^{2}+y ^{2}}\]

solve for y.
x will be \[\sqrt{2^{2}+y ^{2}}\]

Answer 8

where radius = 2

Answer 9

\[138.23=12.56+6.28\times \sqrt{2^{2}+ y ^{2}}\]

Answer 10

how would i solve for y

Answer 11

138.23=12.56+6.26(sqrt(4+y^2))
therefore 138.23-12.56 = 6.28(sqrt(4+y^2))
therefore (138.23-12.56)/6.28 = sqrt(4+y^2)
therefore 4+y^2 = ((138.23-12.56)/6.28)^2
therefore y^2 = (((138.23-12.56)/6.28)^2) - 4
therefore y = sqrt((((138.23-12.56)/6.28)^2) - 4)

Answer 12

so it would be b

Answer 13

no, try again.

Answer 14

nvm i thought we were solving for x

Answer 15

you need to know the value of y to solve for x.

Answer 16

because x = sqrt(r^2+y^2)

Answer 17

y = sqrt((((138.23-12.56)/6.28)^2) - 4).. doing this i got 11.03

Answer 18

lets take this one step at a time:

138.23-12.56 = 125.67
125.67/6.28 = 20.011
20.011^2 = 400.44
400.44-4 = 396.44
y = sqrt(396.44)

Answer 19

19.9.. so e

Answer 20

right, substituting x = sqrt(19.9^2+2^2) = sqrt(400.44) = 20.011 approximately

Answer 21

thank you

Answer 22

you are welcome. It is really easy once you know the formula. it is all a matter of substituting the correct values.