What is theformula for finding the hight of a 30-60-90 degree triangle

We don't know which side your triangle is sitting on, so the 'height'
could be any one of three values.

Here are the two simple tools that tell you everything you want to
know about a 30°-60°-90° triangle.  These are worth memorizing:

-- The side opposite the 30° angle is 1/2 of the hypotenuse.

-- The side opposite the 60° angle is 1/2 of the hypotenuse times √3 .

I memorized them exactly 60 years ago.  They've been very useful,
and as far as I know, they haven't changed.