1. The problem statement, all variables and given/known data If you look at the answer you will see that they integrate sin43x into (sin53x)/5. well, if you can do that why not just integrate 3cos53xdx into (cos63xdx)/2? why go through all the trouble of dividing it into parts? it is true that (cos63xdx)/2 = 0 but i still don't see why you can integrate sin43x and not 3cos53xdx.