



 
Hi Suzanne, It's not the identities themselves that are important it is the experience you gain by working with them. I know very few identities, mainly
There are situations in solving practical problems that involve trigonometry where one of these identities or a different trig identity can help simplify the problem or give another way to look at the problem. Knowledge of these few identities and skill with manipulating identities allows me to see other relationships. Also working with trig identities is one of the few places in the high school curriculum where student are required to construct a mathematical proof. Proofs are at the heart of mathematics and as a mathematician I think it is important that student experience this activity. That being said I don't think trig identities give the optimal experience in proof construction. I don't think this material give much opportunity for ingenuity in the proofs. I would much rather students work with the proofs in Euclidean geometry. Good luck in your studies,  


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