Suppose the trapezoid is ABCD with AB parallel to DC. (It is easier to visualize if you draw it with AB the longer base and the other base DC "above" AB.)
Sketch the altitudes from both C and D - CE and DF. The length of these altitudes is what you want - call it x.
Using right triangle trig, you can get the length of AF in terms of x [tan(A) = x/AF so AF = x/tan(A)] Similarly you can get the length of EB. Since DCEF is a rectangle you know that the length of EF = DC.
Now you can write an equation in terms of x stating that the length of AB equals the length of AF + length CD + length EB.
Now you have an algebra problem. The numbers are probably not pretty, but it is just a linear equation.
-------------- Original message ---------------------- From: tompy97 <email@example.com> > i have a trapazoid of which i know the lengths of the two paralel sides and all > of the angles, is there any way to find the perpendicular height