reference.epsThe above figure shows four possible positions of the angle
--one in each of the four quadrants. Another angle,
, is also marked. This is sometimes called the
*reference angle* for . In each case,
and . Also, ,
recalling that .
The choice of depends upon the
quadrant.

- Quadrant I
- .
- .
- .

- Quadrant II
- .
- .
- .

- Quadrant III
- .
- .
- .

- Quadrant IV
- .
- .
- .

One mnemonic device to remember the signs of the trig functions sine,
cosine and tangent (sine/cosine) in the
four quadrants is **A** **S**mart **T**rig **C**lass:

**A**-
**All**three trig functions are positive in Quadrant I. **S**- Only
**Sine**is positive in Quadrant II; the others are negative. **T**- Only
**Tangent**is positive in Quadrant III; the others are negative. **C**- Only
**Cosine**is positive in Quadrant IV; the others are negative.

Wed Apr 21 08:17:28 EDT 1999