Bunuel
In the xy-plane, at what two points does the graph of y = (x - k)(x + k) intersect the x-axis?
(1) k^2 = 9
(2) k = 3
Target question: At what two points does the graph of y = (x - k)(x + k) intersect the x-axis?Key property: When a line or curve crosses the x-axis, the coordinates of the point(s) of intersection are in the form (x, 0). In other words, the y-coordinate at the point of intersection is 0 Statement 1: k^2 = 9 This tells us that EITHER k = 3 OR k = 3.
Let's consider each possible case:
Case a: k = 3. In this case, the equation becomes y = (x - 3)(x + 3), which means
the graph intersects the x-axis at (3,0) and (-3,0).
Case b: k = -3. In this case, the equation becomes y = (x - (-3))(x + (-3)), which is the same as the equation y = (x + 3)(x - 3). Here,
the graph intersects the x-axis at (-3,0) and (3,0).
So, for both possible cases, we get the same answer to the target question:
the graph intersects the x-axis at (3,0) and (-3,0).
Since we can answer the
target question with certainty, statement 1 is SUFFICIENT
Statement 2: k = 3 In this case, the equation becomes y = (x - 3)(x + 3), which means
the graph intersects the x-axis at (3,0) and (-3,0).
Since we can answer the
target question with certainty, statement 2 is SUFFICIENT
Answer: D
Cheers,
Brent