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#1 2006-11-16 06:39:40

Kiran
Member
Registered: 2006-11-15
Posts: 177

hi

find the volume , to the nearest tenth , of a pyramid that is 6 feet tall and whose base is an equilateral triangle with sides each 10 feet long.

i did
v = 1/3bh
i got
60 feet...help
i got this answer wrong


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#2 2006-11-16 07:49:24

mathsyperson
Moderator
Registered: 2005-06-22
Posts: 4,900

Re: hi

First we need to find the area of the base. You can split the equilateral triangle in half and use Pythagoras to find its height, then work out the area using 1/2bh.

The height works out to be 5√3, so the area of the triangle is 10*5√3/2 = 25√3.

Now we know the base area, we can combine that with the height and work out the pyramid's volume.

V = 1/3 * 6 * 25√3 = 50√3.

That's the exact answer, and by typing that into a calculator we can show that this is 86.6 cubic feet, to the nearest tenth.


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