This is really hard to explain how to do in words, so I will give you physical movements to perform.
For the first one, draw the graph, then rotate the paper. Redraw the graph on another paper, but draw the triangle where it is on the rotated paper.
For the second, draw the graph, then flip the paper. Place the paper on a light source and trace it on the back.
These strategies are much easier than actually mathing through it, and take much less energy and time.
