To make your own triangles: For the 30-60-90 triangle, the hypotenuse is twice the length of the short side. For example, I drew an L with a known good 90-degree angle; measured 10 cm for the short side; and then used my ruler to find where a 20-cm diagonal line would complete the triangle. (The other leg is 10 cm times the square root of 3, but you don’t have to measure or compute that. Just connect the dots.) For the 45-degree triangle, both legs are the same length. (I used 15 cm for mine.) I made a cardboard straightedge to complete the set but didn’t even bother being fussy about whether its edges are parallel to each other; I just needed a straight line to rest the triangles on.