Cosine represents the x-value of the coordinate on the unit circle. The values of cosine at those angles are 0 because they are the points (0,1) and (0,-1).

Sine represents the y-value of the coordinate on the unit circle. The values of sine at those angles are 1 or -1 because they are the points (0,1) and (0,-1).

Tangent represents the y-value/x-value of the coordinate on the unit circle. The values of tangent at those angles are 0 because they are the points (1,0) and (-1,0).

[math]\pi[/math] / [math]180^\circ[/math][br][br]The period of tangent is shorter than the period of sine and cosine. The values repeat more frequently because they are a ratio. In quadrants 2 and 3, there are negative then positive tangent values. In quadrants 4 and 1, there are the same negative and positive tangent values.