if it is not zero. There are many variant ways to write the equation of a line which can all be converted from one to another by algebraic manipulation. The above form is sometimes called the standard form. If the constant term is put on the left, the equation becomes and this is sometimes called the general form of the equation. However, this terminology is not universally accepted, and many authors do not distinguish these two forms. These forms are generally named by the type of information (data) about the line that is needed to write down the form. Some of the important data of a line is its slope, x-intercept, known points on the line and y-intercept. The equation of the line passing through two different points and may be written as If , this equation may be rewritten as or In two dimensions, the equation for non-vertical lines is often given in the slope-intercept form: where: m is the slope or gradient of the line. b is the y-intercept of the line. x is the independent variable of the function . The slope of the line through points and , when , is given by and the equation of this line can be written . Parametric equation Parametric equations are also used to specify lines, particularly in those in three dimensions or more because in more than two dimensions lines cannot be described by a single linear equation. In three dimensions lines are frequently described by parametric equations: where: x, y, and z are all functions of the independent variable t which ranges over the real numbers. (x0, y0, z0) is any point on the line. a, b, and c are related to the slope of the line, such that the direction vector (a, b, c) is parallel to the line. Parametric equations for lines in higher dimensions are similar in that they are based on the specification of one point on the line and a direction vector. As a note, lines in three dimensions may also be described as the simultaneous solutions of two linear equations such that and are not proportional (the relations imply ). This follows since in three dimensions a single linear equation typically describes a plane and a line is what is common to two distinct intersecting planes. Hesse normal form The normal form (also called the Hesse normal form, after the German