SOLUTION: Can you help me solve this expression in order to find out where it is true? {{{ cos(-7pi/2) }}} = {{{ cos(pi + pi/2) }}}

Question 1058785: Can you help me solve this expression in order to find out where it is true?
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Answer by Boreal(15235) (Show Source): You can put this solution on YOUR website!
cos (-7pi/2)=cos(-pi/2)=0, because one can add 2pi multiples without changing the location to get -5pi/2, -3pi/2, and -pi/2
Therefore, cos (pi+pi/2)=0. That is cos (3 pi/2), where it occurs. 270 degrees. ANSWER
It is also cos (pi)*cos(pi/2)-sin (pi)*sin (pi/2)=0
The first is -1*0-0(1)=0, so it is an identity.

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