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Trigonometry : Sum and Difference Identities

Use the sum and difference identities to find the exact value of cos(75) exactly

Which of these is the correct answer?

A. 2 (1- 3)/2
B. 2 (3-1)/2
C. 2 (1- 3)/4
D. 2 (3-1)/4

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Sum and difference identities are investigated. The solution is detailed and well presented. The response was given a rating of "5/5" by the student who originally posted the question.