Measurements of Common Angles/Obtuse Angle

Theorem

An obtuse angle measures $\theta$, where:

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

or:

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

Proof

An obtuse angle is defined to be an angle whose measure is between that of a right angle and a straight angle.

A right angle measures $90 \degrees$ or $\dfrac \pi 2$ and a straight angle measures $180 \degrees$ or $\pi$.

Hence the result.

$\blacksquare$

Sources

• 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): angle