It is also possible to view whether these two trigonometric expressions are congruent by viewing them graphically and numerically. To do this with equation 12 type

and

Then graph the two equations on an appropriate window like Zoom7. Trigonometric to see the two equations are equivalent visually. You can also set up a table and look at the y-values for each equation for a given x value. Notice the y-values are always the same.
 

Check Your Understanding: (Remember to write down the answers to these questions.)

1. Express each degree angle in radians:

a. 270

b. 390

c. 20

2. Express each angle in degrees:
 

a. 

b. 

c. 

3. Use the identities given above to prove the following identities:

a. 

b. 
 

4. View the two identities above both graphically and numerically to see that they are congruent to each other.