A prism is a solid, the sides of which are parallelograms, having its ends equal, and similar plane figures.
Prisms are named according to the number of angles in the base.
A cylinder is a solid, the two ends of which are circular; and it is described, or formed, by the revolution of a right-angled parallelogram about one of its sides, which remains fixed.
To find the superficies of a prism, or cylinder.
Multiply the perimeter of one end of the prism by the length, or height of the solid, and the product will be the surface of all its sides. To which add also the area of the two ends of the prism, when required.
Or, compute the areas of all the sides, and ends separately, and add them all together.
Example.—Required the surface of a cube, whose sides are each 5 inches.
5 + 5 + 5 + 5 = 20, perimeter of one end.
20 × 5 = 100, surface of sides.
5 × 5 = 25, area of one end.
100 + 25 + 25 = 150 square inches. Surface of cube.
To find the surface of a pyramid, or cone.
Multiply the perimeter of the base by the slant height, or length of the side, and half the product will be the surface of the sides; to which add the area of the base when required.