SOLUTION: How do i find an exact value for cos(7pi)?

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Question 703702: How do i find an exact value for cos(7pi)?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
You know that +2%2Api is a complete revolution, so
that +2%2Api+ and +4%2Api+, and +6%2Api+, etc. are all
the same angle.
I can say:
+cos%28+7%2Api+%29+=+cos%28+6%2Api+%2B+1%2Api+%29+
This says that the given angle is +pi+ plus 3 complete revolutions ( no change at all )
+cos%28+7%2Api+%29+=+cos%28+pi+%29+
+cos%28+pi+%29+=+-1+