Find the x-coordinates where f '(x) = 0 for f(x) = 2x + sin(4x) in the interval [0, π].

Question

solomonzelman · Answer

You need to find f'(x), and then to set f'(x)=0, to solve for x-values at which f'(x)=0.

solomonzelman · Answer

What is the derivative of$\tiny~$??
f(x) = 2x + sin(4x)

anonymous · Answer

Sorry had to do some chores

anonymous · Answer

4cos(4x)+2
this is the derivative

anonymous · Answer

cos(4x) = -1/2
 4x=arc cos -1/2
I get to here and then confused where to go next

solomonzelman · Answer

f'(x)=4cos(4x)+2
0=4cos(4x)+2
4cos(4x)=-2
cos(4x)=-1/2

solomonzelman · Answer

anonymous · Answer

Yeah I know that but I feel my teacher will want work shown

anonymous · Answer

Actually Ill just do the intersect in my calculator and explain the logic

anonymous · Answer

would it be possible for you to explain this as well http://prntscr.com/9rxh67 I do not understand it a bit.