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### Orthogonal

Originally, **orthogonality** indicates that two objects form a right angle with respect to each other. It is indicated by placing the ⊥ symbol between the objects.

##### Explanation

Nowadays, we also speak of orthogonal objects when referring to a certain property of these objects.

##### Example 1

In Euclidean geometry, you talk about lines or planes that are **perpendicular** to each other if they make a 90° angle with each other.

##### Example 2

The sine and cosine are orthogonal functions. The cosine is the first coordinate on the unit circle, and the sine is the second coordinate.

##### Example 3

In the Lie group **SO(2)**, the **O** represents a group of rotations in which orthogonality is preserved.

##### Example 4

Modulation techniques used in 4G and 5G cell phone networks are based on the orthogonality of the many subcarriers (from several hundred to several thousand) making up the signal.

## HistoryThe Greek mathematician Euclid described right angles in the book |