so, is -18 the max or the min?
There is a double root at x=1, where it just touches the x-axis.
It crosses the x-axis at x = -4
Since this is a cubic polynomial, with negative leading coefficient, it drops down from the left.
So, it is decreasing on (-∞,-4) and beyond to the minimum.
It comes back up the the x-axis at x=1, so there is a maximum there, as it drops back down.
It continues decreasing on (1,∞).
Somewhere in (-4,1) there is a minimum. In fact, there is a minimum at (-7/3, -500/27). So, the minimum value is -18.5
Why did you pick -2? Just a guess? Not a very useful strategy.
Divide into intervals and evaluate to find the max/min.
f(x)= -(x-1)^2(x+4)
I pick -2
-(-2-1)^2(-2+4)=-18
Is that the correct answer
1 answer
3 answers