how do you find this missing side
Triangles angles always add up to 180 degrees. Add the known degrees togther and subtract from 180 to get what the finall angle is. For example, if a triangle has two known angles, 50 degrees and 80 degrees add them and get 120 then do 180-120 to get the missing angle. hope that helps sorry if it's confusing, Just ask if i need to explain more :)