Hi David

On Wed, 20 Jul 2005 14:13:17 GMT, "David Lang"
wrote:

Hi

I'm building a pergola for my sister in law and my grasp of maths is failing
me.

The roof is an isosceles triangle, e.g. two sides the same and a base.

The angle at the apex is 140 degrees and the two base angles 20 degrees. I
know the size of the base.

How do I calculate the length of the two identical sides and the height from
base to apex?

I seem to recall something about "some officers have, curly auburn hair,
till old age" but I think that only applies to a right angle triangle.

Yup - you're right about the right-angled triangle - but your iso.
triangle can be seen as two right-angled triangles back to back....

The little jingle gives you sine, opp over hypot / cosine adjacent
over hypot and tan opp over adjacent....

So - if you plug in some figures

tan 20 = height / (base divided by 2)
sin 20 = height / long side

or - having got the height, derive the length of the long side by the
old squaw on the hippottamus theorem....

Hope this helps
Adrian

Dave


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