Answer
a. $y= 2cos(x)$
b. See graph.
Work Step by Step
a. Using the Sum Formula, we have $y=sin(x)cos(\pi/2)+cos(x)sin(\pi/2)-sin(x)cos(\pi/2)+cos(x)sin(\pi/2)=2cos(x)$
b. We can graph the new function $y=2cos(x)$ and compare with the given graph to see that they are identical.
