**Trig Circle Chart With Tangent**. The tangent function is negative whenever sine or cosine, but not both, are negative: Sine, cosine and tangent (often shortened to sin, cos and tan) are each a ratio of sides of a right angled triangle:

Try our interactive trig applet. Graphs of the trig functions. The unit circle with tangent is also known as the trigonometric circle of the tangent function.