Question 1058785
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.