Finding X: Positive Values of a Parabola Intersection Problem

Question

The graph of the function below intersects the X-axis at points A and B.

The vertex of the parabola is marked at point C.

Find all values of x x where f\left(x\right) > 0 .

AAABBBCCCX

Step-by-Step Solution

The graph of the parabola intersects the X-axis at points A and B. This tells us these are the roots of the quadratic equation, and that f(x)=0 f(x) = 0 at these points. Given that the shape of the parabola (concave up or down) affects where it is positive or negative:

From the graph:

  • If the parabola opens upwards (which it must, if we are finding f(x)>0 f(x) > 0 outside A and B), it is positive when x<A x \lt A or x>B x \gt B , as the parabola dips below the X-axis between A and B.
  • If the parabola opens downwards, it would be positive between A and B, however, our task is to identify the actual nature based on a graphical interpretation.

The graph signifies the function is positive outside the interval A<x<B A \lt x \lt B .

Therefore, the intervals where f(x)>0 f(x) > 0 are:

x>B x > B or x<A x < A

The answer choice that corresponds to this interpretation is:

x>B x > B or x<A x < A

Answer

x > B or x < A