# Definition:Acute Angle

## Definition

An **acute angle** is an angle which has a measure between that of a right angle and that of a zero angle.

In the words of Euclid:

*An***acute angle**is an angle less than a right angle.

(*The Elements*: Book $\text{I}$: Definition $12$)

### Measurement of Acute Angle

An acute angle measures $\theta$, where:

- $0^\circ < \theta < 90^\circ$

or:

- $0 < \theta < \dfrac \pi 2$