Question 75105
Look at the graph 

{{{graph( 300, 300, -2, 6, -15, 10, x*(x+1)*(x-4) )}}}

x < -1 : f(x) < 0
-1 < x < 0 : f(x) > 0
0 < x < 4 : f(x) < 0
4 < x : f(x) > 0