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.
