Perpendicular definition: Perpendicular simply means 'at right angles'. A line is perpendicular to another if they meet at 90 degrees.
Math Open Reference

Area of a parallelogram. Definition and formula
Math Open Reference

Definition of the midpoint of a line segment.
Math Open Reference

Definition of locus  the shape formed by a set of points that satisfy given crtiteria
Math Open Reference

Definition of a line segment, a line linking two points.
Math Open Reference

Definition and properties of a linear pair of angles  two angles that are adjacent and supplementary
Math Open Reference

An interactive applet that allows you to graphically see the effects of changing the coeeficients in a linear function using sliders
Math Open Reference

Definition of a line
Math Open Reference

Definition of the intersection of two lines
Math Open Reference

Animation showing that in any triangle, the centroid, circumcenter and orthocenter are always collinear  they always lie on a straight line, called the Euler line.
Math Open Reference
