Math Is Fun Forum

anniebelle

Member

Registered: 2009-09-09

Posts: 1

3D Shapes - Trigonometry

In a right square-based pyramid, the length of the side of the square base is 5.7cm. If the angle between the triangular face and the base is 68 degrees, find:

a) height of the pyramid (which I already worked out to be 7.05cm)
b) the angle the sloping edge makes with the base ?

Included is a diagram (: (sorry its a bit blurry, but you get the gist)

Hope you can help me!

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: 3D Shapes - Trigonometry

Hi anniebelle;

I don't understand, which sloping edge? One of the faces of the pyramid? It looks like the drawing is saying that the face is 68° with respect to the base.

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In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

juriguen

Member

Registered: 2009-07-05

Posts: 59

Re: 3D Shapes - Trigonometry

Hi!

I guess the only angle left to calculate with respect to the base is that formed by the edges of the pyramid. This can be done knowing that its projection into the base has length b, that can be computed from the base length a:

Then, the new angle, the height of the pyramid and b can be related:

Hope this is it!
Jose

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“Make everything as simple as possible, but not simpler.” -- Albert Einstein