Remember our initial problem? Given the vehicles heading angle and the displacement, calculate delta x and delta y. Well, you can now solve that problem. But now, instead of thinking about a vehicle and a displacement, we can just think about a right triangle. And this let’s us change our problem statement to this. Given the right triangles reference angle and hypotenuse, calculate the length of the adjacent and opposite sides. And now that we can phrase our driving problem as a triangle problem, we can solve it with trigonometry.