# RECTANGLE

, in Geometry, is a right-angled parallelogram, or a right-angled quadrilateral figure.

If from any point O, lines be drawn to all the four angles of a Rectangle; then the sum of the squares of the lines drawn to the opposite corners will be equal, in whatever part of the plane the point O is situated; viz, . For other properties of the Rectangle, see Parallelogram; for the Rectangle being a species of the parallelogram, whatever properties belong to the latter, must equally hold in the former.

*For the Area of a* Rectangle. Multiply the
length by the breadth or
height.—*Otherwise;* Multiply
the product of the two diagonals
by half the sine of their angle at
the intersection.

That is, AB X AC, or AD X BC X 1/2 sin. [angle]P = area. A Rectangle, as of two lines AB and AC, is thus denoted, AB X AC, or AB . AC; or else thus expressed, the Rectangle of, or under, AB and AC.

Rectangle, in Arithmetic, is the same with product
or factum. So the Rectangle of 3 and 4, is 3 X 4
or 12; and of *a* and *b* is *a* X *b* or *ab.*