## anonymous 5 years ago Hello! Not quite sure about how to find derivative of: y = 3x - 5cos('pi'x)^2

1. anonymous

3x prime=3, -5cos(u)^2= 10sin(u)*u prime= 3+10sin(pi*x)*pi

2. anonymous

y'=3-5*2*cos(pi*x)*pi*(-sin(pi*x))=3+5pi*sin(2pix)

3. anonymous

dellcom, you forgot that (cos^2)'=2cos*(-sin).... :)

4. anonymous

OK, so I use the chain use. But I'm still missing something. The answer I get is: $y = 3 + 10\cos \pi x \sin \pi x$ Its seems like you combined something that I am not seeing..