1) express as a sum or difference as it applies to: sin(5x)sin(3x)

2) find the exact value in radical form for: cos(45)cos(15)

I'm not sure if I'm supposed to put two questions in one thread, but i thought that maybe they were worked similarly so I could lump them together. Also, the integers in problem two are in degrees, not radians. And I think that I'm supposed to use identities to solve these but I'm not sure which one.

Thanks ahead of time. This site is very, very helpful.