SOLUTION: prove that the given equation is an identity cos(pi +x)=-cosx

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Question 1163194: prove that the given equation is an identity
cos(pi +x)=-cosx
Answer by Alan3354(69443) About Me  (Show Source):
You can put this solution on YOUR website!
prove that the given equation is an identity
cos(pi +x)=-cosx
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cos(A+B) = cos(A)*cos(B) - sin(A)*sin(B)
Sub pi and x for A & B