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Cosine Identity

In the applet below, the graph of the function is displayed. Place the BIG WHITE POINT anywhere you'd like prior to sliding the slider. Answer the question that follows.


Write a new trigonometric identity that expresses the relationship between and .


What else can you conclude about the parent cosine function ? For a hint, click here.

Quick Demo: 0:36 sec to 1:05 sec (BGM: Andy Hunter)