Verifying Trig Identities
If you need to determine if an equation is a trigonometric identity, you
can use your graphing calculator. A "formal proof" of a
trigonometric identity is done algebraically. The graphing
calculator, however, can be used to "check" your work.
Determine if cos^{2} x = 1  sin^{2} x is a trig
identity: 
Enter the left side in
Y1.
Enter the right side in Y2.
Set the bubble animation for the second graph.

Choose ZOOM #7 ZTRig 
If the bubble runs over the same graph as
the first plotting, the equation is a trig identity.

2nd GRAPH (TABLE)

The TABLE
can also be used to check to see if the results are the same
from both graphs. Arrow up and down to see if the values
listed under columns Y1 and
Y2 remain the same. Adjust your table through 2nd WINDOW (TBLSET)
to see more varied values. 
Answer: Yes, cos^{2} x = 1  sin^{2} x is a trig
identity.
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