Secant of Three Right Angles

Theorem

 * $\sec 270 \degrees = \sec \dfrac {3 \pi} 2$ is undefined

where $\sec$ denotes secant.

Proof
But from Secant of Right Angle, $\sec 90 \degrees$ is undefined.

Also see

 * Sine of Three Right Angles
 * Cosine of Three Right Angles
 * Tangent of Three Right Angles
 * Cotangent of Three Right Angles
 * Cosecant of Three Right Angles