"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.

Dave


Not totally with you on this Dave, but here goes with some sort of an
explanation. :-)

The angle at the apex is nearly a straight line when it's 140 degrees, so
you'll have to go a hell of a long length to reach the base with your beams
if you want a structure that average people can walk under.

What you need are vertical uprights which will support the roof at the
angles you want to make. So start by fixing uprights to the height of the
average person, say 2.1 mtrs, then build your roof on top of these at the
angles you say you need. You should then end with a structure that will
look pretty and be high enough to walk through without banging heads.