Ok, so the rough estimate of a diagonal of a square is 1.5 the side... but I use a calculator for this. The typical quilting triangle is a Right angle. That is there are two sides that are the same dimension, one 90 degree angle and two 45 degree angles. Since you have the diagonal, that's the hypotenuse (33) and you know the angles, so I used option 4 on the link.
http://www.analyzemath.com/Geometry_...alculator.html
This site works if you know any of the various parts, it says the it's roughly 24" (23.33) for the other two sides, add 1" to cut with (the exact math is 7/8"), so (2) 25" squares will make your 4 setting triangles, plus a tiny bit to trim down.