Someone please help with surface area of pyramids and cones

- anonymous

Someone please help with surface area of pyramids and cones

- katieb

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- anonymous

are these answers correct?
the first one i got 282.6m^2
the second one i got 175.84in^2

##### 2 Attachments

- amistre64

if you can cut the cone up its lengthand make into part of a circle, the surface area is easy to get :) maybe even easy if I think about it some

- amistre64

is the 10 inches the length up the side of the cone or the height?

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## More answers

- anonymous

length

- anonymous

its actually slant height

- amistre64

then that 10 inch length is the radius of a larger circle, find its circumference"
2pi10 20pi is its curcumference
the small base circle is the length of the circumference that you want to find an area for
2pi4 = 8pi
make sense?

- anonymous

kinda

- anonymous

\[s =\pi \times r ^{2}+\pi \times r \times l\] is the formula i need to use

- amistre64

length of an arc = theta(r)
8pi = theta(10)
theta = 8pi/10 = 4pi/5
area of sector = theta r^2/2
(4pi/5)(10)(10)/2
200/5 = 40pi fpr the surface area of the cone, do we include that base in this or not?

- amistre64

40pi + 16pi = 56pi if I did it right :)

- anonymous

ok

- anonymous

would = 175.84in^2

- amistre64

175.92 is what I get... is that close enough?

- amistre64

175.84 if you use (3.14)

- anonymous

yea

- anonymous

how would i find the surface area of this one

##### 1 Attachment

- amistre64

if im doing it right, I get 85pi

- anonymous

would i use half the diameter?

- amistre64

if you dont have answers to check against, I would suggest gettting a second opinion :)
but yes, radius is half the diameter

- anonymous

\[s =\pi \times 5^{2}+\pi \times 5 \times 12\]

- amistre64

i got 25pi + 60pi too :)

- amistre64

im glad the formula works :)

- anonymous

witch would = 266.9ft^2

- anonymous

would you please help me with three more

- amistre64

i could try.... getting kinda deer in the headlights feeling....must.....carry.........on. . . . . . . ok

- anonymous

find the surface area of the regular pyramid

##### 3 Attachments

- amistre64

#31 3cm is pointing to what?

- anonymous

3cm is height i believe

- amistre64

is it face height or pyramid height?

- anonymous

the formula for this on is S=B+1/2Pl

- anonymous

looks like pyramid hight

- amistre64

pyramid height would have a dotted line stricking down the middle of it..... i think its face height.

- anonymous

so do i

- amistre64

4cm^2 + 12 cm^2 = 16 cm^2 for #31

- amistre64

#32...all I see is a 7 and not much else for details...

- anonymous

thats all there is

- amistre64

is that all sides are 7? like an equalateral triangle?

- anonymous

yea

- amistre64

then I would do:
4 times (1/2)(49)sin(60)
84.87 m^2

- amistre64

if you have a side-angle-side, the area can be determined by:
(side)(side)(sin(angle))/2 and there are 4 sides so I timesed it by 4 :)

- amistre64

(side)sin(a) = height, and the other side = base

- anonymous

ok

- amistre64

and for the last one its just like the first except with decimals..

- amistre64

(9.2)^2 + 4(9.2)(13)/2

- amistre64

84.64 + 239.2 = 323.84

- anonymous

okay thank you so much

- amistre64

youre welcome :)

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