# Definition:Obtuse Angle

## Definition

An **obtuse angle** is an angle which has a measurement between those of a right angle and a straight angle.

In the words of Euclid:

*An***obtuse angle**is an angle greater than a right angle.

(*The Elements*: Book $\text{I}$: Definition $11$)

Note that Euclid did not consider the concept of reflex angles.

### Measurement of Obtuse Angle

An obtuse angle measures $\theta$, where:

- $90^\circ < \theta < 180^\circ$

or:

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