SOLUTION: Can you Proof the following Identity? CosA cos(-A)- sinAsin(-A)=1

Question 747302: Can you Proof the following Identity?
CosA cos(-A)- sinAsin(-A)=1
Found 2 solutions by tommyt3rd, josgarithmetic:
Answer by tommyt3rd(5050) (Show Source): You can put this solution on YOUR website!
in the equation

we notice the evenness and oddness of cosine and sine:

and

therefore...

:)
Answer by josgarithmetic(39630) (Show Source): You can put this solution on YOUR website!
Using symmetry of the functions, , and . Check on the Unit Circle to be sure this makes sense.

Those facts let us say this step.

=
=
DONE.
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