The simplest geometric idea is the point, and then the line, the plane, and the solid. Shapes like circles, squares, rectangles, and triangles are flat, and we can think of them as being parts of a plane, flat like a drawing. Shapes like spheres, cubes, and pyramids are solid, and we can think of them as being part of the whole universe - as indeed any real object is.
Trigonometry is the science of angular magnitudes and the art of applying the principles of this science to the solution of problems.
