SOLUTION: Can you find the answer to sin (21pi/12) using sum and difference identity?

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Question 1064447: Can you find the answer to sin (21pi/12) using sum and difference identity?
Answer by ikleyn(52915) About Me  (Show Source):
You can put this solution on YOUR website!
.
  sin%2821pi%2F12%29 = -sin%28%2821-12%29%2Api%2F12%29   (is it clear to yo ? )


= -sin%289pi%2F12%29 = -sin%283pi%2F4%29 = -sin%28pi%2F4%29    (is it clear to you ?)


= -sqrt%282%29%2F2.