Stretch out your right hand, let your thumb and forefinger form an "L" shape, with your thumb to the right, your forefinger up, and the rest of your fingers pointing forward, thus establishing the right hand coordinate system. Among them, thumb, forefinger and other fingers represent the positive directions of X, Y and Z axes respectively.

In the spatial rectangular coordinate system, let the thumb of the right hand point to the positive direction of the X axis and the index finger point to the positive direction of the Y axis. If the middle finger can point in the positive direction of the Z axis, this coordinate system is called the right-handed rectangular coordinate system. On the contrary, it is a left-handed rectangular coordinate system.

Spatial rectangular coordinate system: cross the fixed point O and make three mutually perpendicular number axes, all of which take O as the origin and generally have the same length unit. These three axes are called X axis (horizontal axis), Y axis (vertical axis) and Z axis (vertical axis) respectively. Generally called the coordinate axis. Usually, the X-axis and Y-axis are arranged on a horizontal plane, while the Z-axis is a vertical line. Such three coordinate axes form a spatial rectangular coordinate system, and point O is called the coordinate origin.

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