**Trig Functions of Angles**

a) Recall that the sine function is positive in Quadrants I and II, the cosine function is positive in Quadrants I and IV, and the tangent function is positive in Quadrants I and III.

b) In addition, the reference angle for is

1. , if .

2. , if .

3. , if .

4. , if .

c) If is an angle in standard position, and is a point on the terminal side of (other than the origin), then

and

where

**Ex 1** Find .

**Sol** The reference angle for is
.
Since the sine is negative in Quadrant IV,
.

**Ex 2** Find .

**Sol** The reference angle for is
.
Since the cosine is negative in Quadrant III,
.

**Pr 1** Find .

**Pr 2** Find .

**Pr 3** Find .

**Pr 4** Find .

**Pr 5** Find .

**Pr 6** Find .

**Pr 7** Find .

**Pr 8** Find .

**Pr 9** If is an angle in standard position with the point
on its terminal side, find and .

**Pr 10** Find .

**Pr 11** Find .

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