Measurements of Common Angles

Theorem

Full Angle

A full angle is equal to $360 \degrees$ or $2 \pi$ radians.

Straight Angle

The measurement of a straight angle is $180 \degrees$ or $\pi$ radians.

Right Angle

The measurement of a right angle is $\dfrac {180 \degrees} 2 = 90 \degrees$ or $\dfrac \pi 2$.

Acute Angle

An acute angle measures $\theta$, where:

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

or:

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

Obtuse Angle

An obtuse angle measures $\theta$, where:

$90 \degrees < \theta < 180 \degrees$

or:

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

Reflex Angle

A reflex angle measures $\theta$, where:

$180 \degrees < \theta < 360 \degrees$

or:

$\pi < \theta < 2 \pi$