# Definition:Engineering Notation

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## Definition

### Euclidean 2-space

Define the ordered 2-tuples:

\(\ds \mathbf i\) | \(=\) | \(\ds \tuple {1, 0}\) | ||||||||||||

\(\ds \mathbf j\) | \(=\) | \(\ds \tuple {0, 1}\) |

From Standard Ordered Basis is Basis, we have that any vector in $\R^2$ can be represented by:

- $c_1 \mathbf i + c_2 \mathbf j$

where $c_1, c_2 \in \R$.

This way of presenting vectors is called **engineering notation**.

### Euclidean 3-space

Define the ordered 3-tuples:

\(\ds \mathbf i\) | \(=\) | \(\ds \tuple {1, 0, 0}\) | ||||||||||||

\(\ds \mathbf j\) | \(=\) | \(\ds \tuple {0, 1, 0}\) | ||||||||||||

\(\ds \mathbf k\) | \(=\) | \(\ds \tuple {0, 0, 1}\) |

By the same logic as the above definition, we can write any vector in $\R^3$ as:

- $c_1 \mathbf i + c_2 \mathbf j + c_3 \mathbf k$

where $c_1, c_2, c_3 \in \R$.

Note that $\mathbf i$ and $\mathbf j$ take on a different meaning in $3$-space than in $2$-space.

### Euclidean $n$-space

In higher dimensions, rather than writing $\mathbf l, \mathbf m, \mathbf n$, and so on, the convention is to use:

\(\ds \mathbf e_1\) | \(=\) | \(\ds \tuple {1, 0, 0, \ldots, 0, 0}\) | ||||||||||||

\(\ds \mathbf e_2\) | \(=\) | \(\ds \tuple {0, 1, 0, \ldots, 0, 0}\) | ||||||||||||

\(\ds \) | \(\vdots\) | \(\ds \) | ||||||||||||

\(\ds \mathbf e_n\) | \(=\) | \(\ds \tuple {0, 0, 0, \ldots, 0, 1}\) |

Then any vector in $\R^n$ can be expressed as:

- $c_1 \mathbf e_1 + c_2 \mathbf e_2 + \cdots + c_n \mathbf e_n$

where $c_1, c_2, \cdots, c_n \in \R$.

This convention is also frequently seen for $2$-space and $3$-space.

## Also denoted as

Particularly in hand-written material, it is common to put a circumflex above the letters, as is common to do with other unit vectors:

- $\hat \imath, \hat \jmath, \hat k$

With such a notation, they may be referred to as **$i$-hat**, **$j$-hat**, and **$k$-hat**.

The "hat" can be used as a diacritic in addition to or instead of the dots above the letters $i$ and $j$.

## Sources

- For a video presentation of the contents of this page, visit the Khan Academy.