"David Lang" wrote in message
...
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.

If you drop a perpendicular down from the apex you have two right angled
triangles and can work from there.

If the base is 2B and half the base length is B, then

the vertical will be B x tangent(20deg)
the sloping edge will be B / cosine(20deg)

Bob Mannix