Anyone good with Trigonometry???

I need an answer to a question and i just can't get a close answer with any formula i find! sooo.. here it is.. if anyone can help thatd be awesome!!

What is the volume of a frustrum of a right pyramid with the area of the lower base equal to 100 sq in., the area of the upper base equal to 25 sq in., and the altitude equal to 12in.???

O_O Whats a frustrum...

and what is a right pyramid????

I am curious to see what a left pyramid looks like because I thought all pyramids were you know.. four sided and pointy..

edit: Oh I get it, it has a flat top...

well first you will want to find the area of the whole thing.....

no clue how you do that.. but you have to combine the three numbers in an equation somehow.. if it was a regular triangle/pyramid I would suggest using th epyramid area finder thing but since it isnt I have no clue

once you get the area though you should be able to covert it into volume...

to be honest I dont think I ever did pyramids with two bases in trigonometry...

well the formula i found is V=(altitude/3) ((lower base x lower base) + (upper base x upper base) + the square root of (upper base x upper base) x (lower base x lowerbase)) but that gives me a number WAAAAY out of what my four choices are... lol and that formula was off of a website with a picture of the pyramid and everything... Gaaah!!! Im so frusterated!

I'm doing Trig next term! Wouldn't have a clue what it is!

Sorry! & good luck!

Have a link to the website?

Spotz

its not a website Johns an apprentice carpenter and he has books he has to do for it, kind of like college at home. He's behind on books so Im trying to help him and they sent us trig and geometry books. Neither of us has ever taken trig and the little books they sent us are no help at all.

Let me rephrase...

Originally Posted by RoyalEnchntrss

ol and that formula was off of a website with a picture of the pyramid and everything

Click to expand...

Originally Posted by Spotz

Have a link to the website?

Click to expand...

Spotz

ohhhh lol sorry! No i dont but i found another one for you.. its got the same stuff on it ...

http://mathworld.wolfram.com/PyramidalFrustum.html

If what I am finding is correct...then the answer should be 700 cubic inches.

I see the problem you are having with the formula you found. It operates on the concept that you don't have the area of the bases, but rather the dimensions.

To get the area of the bases, you would multiply the dimension of one lateral side by the dimension of the adjacent perpendicular side.

Since you already have the area's, the formula should be:

[height]/3*([area of base one]+[area of base 2]+SquareRoot([area of base one]*[area of base 2]))

or in this case:

12/3*(100+25+SqRt(100*25))
4*(125+SqRt(2500))
4*(125+50)
4*175
700

Does that make any sense?

Spotz

If the question was instead:

What is the volume of a frustrum of a right pyramid with the the lower base a square of 10 inches, the upper base a square of 5 inches, and the altitude equal to 12in.???

Then you would need to use the formula you found, because you need the area of each base.


H = Height
B1 = Base 1 Area
B2 = Base 2 Area
W1 = Base 1 Width
W2 = Base 2 Width
L1 = Base 1 Lenght
L2 = Base 2 Length

So if you have the area the formula is:

H/3*(B1+B2+SqRt(B1*B2))

If you have the dimensions of the base the formula is:

H/3*((L1*W1)+(L2*W2)+SqRt((L1*W1)*(L2*W2)))


Hope that made some sense,

Spotz

yes! i see what i did wrong.. lol my cousin got the same answer just now and he's an accountant so thats the answer Im putting down! thank you sooo much.

Welcome

Spotz

you guys rock lol