ok

f"(x) = 9x

9x=0

x=0

take two values of x one more than 0 and the other less than 0

f"(1)=9 positive then f is concave up at [0,infinity)

f"(-1)= -9 negative then f is concave down at (- infinity , 0]

and I attack the graph as you can see the function is increasing from infinity to -2 and from -2 to 2 decreasing and more than 2 increasing and the point (0,0) you see that the curve change the concavity

so if you want to sketch you should first put the critical points and the inflection points then see the interval of increasing and decreasing and the concavity I write a lot of words

Attachment 11396