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:

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

or:

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

Sources

• 1989: Ephraim J. Borowski and Jonathan M. Borwein: Dictionary of Mathematics ... (previous) ... (next): acute: 1. (of an angle)
• 1998: David Nelson: The Penguin Dictionary of Mathematics (2nd ed.) ... (previous) ... (next): acute angle
• 1998: David Nelson: The Penguin Dictionary of Mathematics (2nd ed.) ... (previous) ... (next): angle
• 2008: David Nelson: The Penguin Dictionary of Mathematics (4th ed.) ... (previous) ... (next): acute angle
• 2008: David Nelson: The Penguin Dictionary of Mathematics (4th ed.) ... (previous) ... (next): angle
• 2014: Christopher Clapham and James Nicholson: The Concise Oxford Dictionary of Mathematics (5th ed.) ... (previous) ... (next): acute angle
• 2021: Richard Earl and James Nicholson: The Concise Oxford Dictionary of Mathematics (6th ed.) ... (previous) ... (next): acute angle