Axis

x-Axis

The x-axis is the horizontal axis on a two variable Cartesian graph. This axis is typically assigned to the input of the function being represented. This also means that the x-axis typically represents the independent variable.

y-Axis

The y-axis is the vertical axis on a two variable Cartesian graph. The y-axis is typically assigned to the output of the function being represented. This also means that the y-axis typically represents the dependent variable.

On a three-variable Cartesian system, the y-axis typically represents an independent variable.

z-Axis

The z-axis is the third axis on a three variable Cartesian graph. The z-axis is typically assigned to the output of the function being graphed. This also means that it shows the dependent variable.

Axis of Symmetry

An axis of symmetry is the line around which a curve is symmetrical.^[4] For parabolas this is a line which passes through the vertex (see figure 6).

Functions and their inverses can also be drawn using the axis of symmetry, which is the line with the equation y = x (see figure 7).

Real Axis

In the complex plane, the real axis, on which real numbers are represented, is the horizontal axis.^[3]

Imaginary Axis

In the complex plane, the imaginary axis, on which imaginary numbers are represented, is the vertical axis.^[3]

Axis of Rotation

An axis of rotation is a line about which a geometric object rotates.^[5] The earth is an example of a rotating sphere. The line from the north pole to the south pole is the axis of rotation as show in figure 10. The earth spins, or rotates, about the axis of rotation.