The square means the angle is 90 degrees. Therefore, for the big triangle, we already know 2 of the degrees, 50 and 90. A triangle's degrees add up to 180. 50+90=140. 180-140=40. This means the top angle is 40. Now finding X is easy, because we already know the other 2 points in the triangle, which are 38 and 40. Add those up, you get 78. 180-78=102, your answer. The triangle is 102 degrees.
Since the value of all angles within a triangle must equal 180 degrees, if you know at least two angles, you can subtract them from 180 to find the missing third angle. If you are working with equilateral triangles, divide 180 by three to find the value of X.
