Sin, Cos and Tan

Quadrants and the "cast" Rule

On a set of axes, angles are measured anti-clockwise from the positive x-axis. So 30° would be drawn as follows:

The angles which lie between 0° and 90° are said to lie in the first quadrant. The angles between 90° and 180° are in the second quadrant, angles between 180° and 270° are in the third quadrant and angles between 270° and 360° are in the fourth quadrant:

...