(x+13)(x-18)(x+4)>0
I cannot figure this one out. Please help.
This is a cubic polynomial with zeroes at x=-13, x=-4 and x=18.
The coefficient of the x³ term being positive, f(x)<0 when x-> -∞ and f(x)>0 when x->∞.
Thus f(x) >0 when x is between the first two roots and greater than the third root, namely on the interval:
(-13,-4)∪(18,∞)