In Try This 3 you determined the exact value for 
You may have used the unit circle, reference triangles, or some other process to determine the value of the trigonometric ratio. Determining Exact Values for Trigonometric Ratios will demonstrate using the unit circle or reference triangles to determine the exact values for trigonometric ratios.
Watch Determining Exact Values for Trigonometric Ratios to see how to determine the exact value of sec 
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You can calculate approximate values for trigonometric ratios by using your calculator.
Your calculator can determine the trigonometric values for angles measured in degrees or radians. You will need to choose the correct mode for your calculator. Check your calculator manual to change from degree to radian mode and back again. For example:
you would use radian mode. So, 
= 0.965 925 826…Most calculators do not have cosecant, secant, or cotangent buttons. You can still calculate the value of these ratios by using your calculator.
Example
Determine the approximate value of sec (−4.1), and round your answer to four decimal places.
Solution
For this question, your calculator should be in radian mode since −4.1 is a radian measure. Remember, when there is no degree symbol, assume the angle is measured in radians.
In which quadrant would the angle −4.1 terminate?
The angle terminates in quadrant 2. The value of the cosine ratio is negative in quadrant 2 because the value of the x-coordinate is negative in quadrant 2. If the cosine ratio is negative, the value of the secant ratio will also be negative.
If you did not get this answer, check to see if your calculator is in radian mode.
Add the following terms to your copy of Glossary Terms:
Add the following formulas to your copy of Formula Sheet:
