ellipse is the locus of a point that moves such that the sum of its distances from two fixed points called the foci is constant. An ellipse can be drawn by sticking two pins in a sheet of paper, tying...ellipse is the locus of a point that moves such that the sum of its distances from two fixed points called the foci is constant. An ellipse can be drawn by sticking two pins in a sheet of paper, tying a length of string to the pins, stretching the string taut with a pencil, and drawing the figure that results. During this process, the sum of the two distances from pencil to one pin and from pencil to the other pin remains constant and equal to the length of the string.
