# Definition:Altitude of Triangle

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## Definition

Let $\triangle ABC$ be a triangle.

Let a perpendicular be dropped from $\angle A$ to its opposite side $a$:

The line $h_a$ so constructed is called the **altitude** of $\angle A$.

### Foot of Altitude

The point at which $h_a$ meets $BC$ is the **foot of the altitude $h_a$**.

## Also defined as

The word **altitude** is often used to mean the **height** of a triangle.

However, on $\mathsf{Pr} \infty \mathsf{fWiki}$ it is preferred if the terms **altitude** and **height** are used specifically to mean the perpendicular and its length, to avoid confusion.

## Also see

Altitudes are a type of Definition:Cevian.

## Sources

- 2014: Christopher Clapham and James Nicholson:
*The Concise Oxford Dictionary of Mathematics*(5th ed.) ... (previous) ... (next): Entry:**altitude**