1.1 Angles in Standard Position

Notes

An angle is formed by rotating a ray (the terminal side) from a starting ray (the initial side). In standard position the vertex is at the origin and the initial side lies on the positive $x$-axis.

• Counterclockwise rotation gives a positive angle; clockwise gives a negative angle.
• The axes split the plane into Quadrants I to IV: $0^\circ$ to $90^\circ$ is Quadrant I, $90^\circ$ to $180^\circ$ is II, $180^\circ$ to $270^\circ$ is III, $270^\circ$ to $360^\circ$ is IV.
• A quadrantal angle has its terminal side on an axis: $0^\circ, 90^\circ, 180^\circ, 270^\circ$ and so on.
• A degree splits into 60 minutes, and a minute into 60 seconds: $35.5^\circ = 35^\circ 30'$.