Question

Use the parabola tool to graph the quadratic function f(x)=(x−4)(x+2). Graph the parabola by first plotting its vertex and then plotting a second point on the parabola.

Answer 1

If the eqn of the parabola is f(x) = (x-4)(x+2), we need to mult. this out to find the coordinates of the vertex.

Then f(x) = x^2 + 2x - 4x - 8, and f(x) = x^2 - 2x - 8.

One way in which you can find the vertex is to calculate x = -b / (2a). Here, that comes to

-(-2)
x = ---------- = 1. f(1) = 1^2 - 2(1) - 8 = - 9. Vertex is at (1, -9).
2(1)

Find another point on the curve: Let x=0, for which y=-8. Then (0, -8) is on the curve. Plot the vertex and this point and draw a smooth parabola thru both.

Answer 2

Here are a bunch of CORRECT answers, your answer is somewhere in there. For the first CORRECT answer the second point is -5,-9. Don't make the same mistake I did on question 3, but it still shows the correct answer. I love to help.