# 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.

### Measurement of Acute Angle

An acute angle measures $\theta$, where:

$0 \degrees < \theta < 90 \degrees$

or:

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