for $\displaystyle y= x^3-9x^2+27x$

from the first derivative $\displaystyle y'=3x^2-18x+27$

If found the critical no x = 3

and attempted the 1st deriv. test (-inf,3)(3,inf)

and tested with points 1,4 and got two positives does this mean I have to try with the 2nd derivative

$\displaystyle y''=6x-18$

I'm confused with what I do next....