The Purplemath Forums

Q: Let f(x)=20x-10sin(4x) for 0<=x<=pi/2 Find the largest interval(s) over which the function f is increasing or decreasing. I tried to solve this: f'(x)=20-40cos(4x) =20(1-2cos(4x)) on keeping f'(x)=0, i get x=pi/12 I just cannot get correct intervals to work properly with my online math homework s...

I did differentiate that! The problem is with the intervals!


Could you please solve it?


Thank you!

Sorry to bug you again but my function was f(x)=20x-10sin(4x)
After taking the derivative I get f'(x)=20-10*4*cos(4x) = 20-40cos(4x)

So, I did take the derivate of 4x!

Matt, thanks a zillion!