Express 3cos(x)+4sin(x) in the form Rsin(x+y) where you should explicitly determine R and y.

Since Rsin(x+y)=Rsin(x)cos(y)+Rsin(y)cos(x), we can set Rcos(y)=4 (1) and Rsin(y)=3 (2) on comparison to the desired equation. Considering (2) divided by (1) we see that tan(y)=sin(y)/cos(y)=3/4 so y=atan(3/4). Considering (1)^2+(2)^2 we see that R^2=25 so R=5 and we are done.