# Math Help - Intervals of Increase and Decrease

1. ## Intervals of Increase and Decrease

The function is 3x-9sin(x), 0<x<pi

I found the derivative which is 3- 9cos(x)

Now how would I find the open intervals of increase and decrease given the domain 0<x<pi as seen above?

2. Originally Posted by ctran
The function is 3x-9sin(x), 0<x<pi

I found the derivative which is 3- 9cos(x)

Now how would I find the open intervals of increase and decrease given the domain 0<x<pi as seen above?
Set the derivative equal to 0. Figure out what angle corresponds to that in the domain of 0 to pi, as well as any possible repeats.

3. Originally Posted by Jameson
Set the derivative equal to 0. Figure out what angle corresponds to that in the domain of 0 to pi, as well as any possible repeats.
I did this and found one angle which is arccosine(1/3), how would I go about finding other solutions within this domain?