Definition:Acute Angle

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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:

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


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