i dont how to do this and i can't figure it out
Determine the x values where F(x) is positive
f(x)=x^(3)-9x
determine the x values where f(x) is increasing
f(x)=x^(2)-2x-8
Hi ducktrix,
Welcome to MHF!
In the future please post one problem per thread and show all attempted work so we know what you know.
For #1, first factor this. $\displaystyle x^3-9x=x(x^2-9)=x(x+3)(x-3)$
You should be able to tell that the three zeros of f(x) are 0, 3 and -3. So draw a number line and mark these three points on it. Now the regions inbetween these values will either be positive or negative. Choose a test point to see. Make sense?