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Mathematics 22 Online
OpenStudy (anonymous):

find the lateral area, volume and total area

OpenStudy (marissalovescats):

Alrighty let's see the picture

OpenStudy (anonymous):

OpenStudy (marissalovescats):

This is a hexagonal pyramid. Lateral Area of that is: \[3a \sqrt{h^2+\frac{ 3a^2 }{ 4 }}\] Where a is base edge and h is the height

OpenStudy (anonymous):

ok one sec let me solve

OpenStudy (mosaic):

I think in the diagram, the 6 looks like it is the height of the triangle and not the height of the pyramid. If that is the case, all you have to do is find the area of one triangle and multiply it by 6 to get the lateral surface area.

OpenStudy (anonymous):

really?!

OpenStudy (anonymous):

so 72?

OpenStudy (mosaic):

Well, if I take 6 to be the height of the triangle, then the area of one triangle = 1/2 * base * height = 1/2 * 4 * 6 = 12. Multiply that by 6 for the six triangles and you get 72 as the lateral surface area. If that is wrong then you can try the above formula by marissa.

OpenStudy (anonymous):

no its right! now i need the volume? and total area

OpenStudy (anonymous):

marissa u still there?

OpenStudy (mosaic):

For the total area just add the area of the hexagon base to the lateral surface area.

OpenStudy (anonymous):

how do u find the area of a hexagon?

OpenStudy (mosaic):

Area of hexagon = \(\Large \frac {3\sqrt{3}}{2}a^2\) where 'a' is the side of the hexagon.

OpenStudy (anonymous):

how does it come out to be in the form of __+__ square root _?

OpenStudy (mosaic):

Put a = 4 in the above formula to calculate the area of the hexagonal base. To that add 72, the lateral surface area calculated earlier.

OpenStudy (anonymous):

3 squareroot 3 over 32?

OpenStudy (mosaic):

put a = 4: \(\Large \frac {3\sqrt{3}}{2}a^2 = \frac {3\sqrt{3}}{2}16 = 24\sqrt{3}\). Total surface area = \(\Large 72 + 24\sqrt{3}\)

OpenStudy (anonymous):

how u get 24?

OpenStudy (mosaic):

a = 4, a^2 = 16. divided by 2 is 8. multiplied by 3sqrt(3) = 24sqrt(3).

OpenStudy (anonymous):

o got it!!! thank u! so how do i find the volume?

OpenStudy (mosaic):

Volume of a pyramid = 1/3 * area of base * height of the pyramid.

OpenStudy (anonymous):

so \[ 24\sqrt{3}*6\]?

OpenStudy (mosaic):

1/3 * 24 * sqrt(3) * height of the pyramid. You have to use Pythagoras theorem to find the height of the pyramid. The 6 in the diagram is the height of the triangle and not the height of the pyramid.

OpenStudy (anonymous):

o ok thank you

OpenStudy (mosaic):

You are welcome.

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