Measurements of Common Angles/Right Angle

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

Proof
A right angle is equal to one half of a straight angle.

From Measurement of Straight Angle it follows that the measurement of a right angle is $\dfrac{180^\circ} 2 = 90^\circ$ or $\dfrac \pi 2$.