Solid angle orientation formula_9, and distance from the viewer as: where the surface area of a sphere is . The solid angle of a cone with its apex at the apex of the solid angle, and with apex angle 2, is the area of a spherical cap on a unit sphere For small such that , this reduces to the area of a circle . The above is found by computing the following double integral using the unit surface element in spherical coordinates: This formula can also be derived without the use of calculus. Over 2200 years ago Archimedes proved that the
Solid body against. This allows musicians to stop the string in the same place. Ebony, rosewood and maple are commonly used to make the fingerboard. Some electric guitar necks do not have a separate piece of wood for the fingerboard surface. All the solid bodies have variations in scale length or, the length of the strings from the nut to the bridge. The action, or the height of the strings from the fingerboard, is adjustable on solid body instruments. Most solid bodies have controls for volume and tone. Some have an electronic preamplifier with equalization for low, middle, and high frequencies. These