# Vector Arithmetic and Vector Drawings [8/10]

This program combines two circular motions into a single motion. In this case, both circular motions have the same amplitude equal to 150.

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-- Orientations of Coordinate Systems --

The coordinate system commonly used in 2D computer graphics has the y-coordinate increasing downwards. This would be quite unusual in common mathematics, where the y-coordinate commonly increases upwards.

One of the consequences of this discrepancy reflects in the direction of rotation. In 2D computer graphics, the positive rotation (i.e. a rotation by a positive angle) is in the clockwise direction, while in common mathematics the positive rotation is anti-clockwise.

The choice of this coordinate system for 2D computer graphics is due to the scanning direction of electron guns in old televisions. A television's electron gun scans the screen from left to right and from top to bottom.

In any number of dimensions, two orientations of coordinate systems are possible. A long time ago, those two orientations were given some arbitrary names by mathematicians. The orientation of common 2D coordinate system in mathematics is called the right orientation, while the orientation of the coordinate system in 2D computer graphics is called the left orientation.

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