Matt@VeritasPrep wrote:Brent@GMATPrepNow wrote:As Rich mentioned, you don't need to know how to find the equation of a parabola on the GMAT. All that matters is that parabolas are symmetrical about an axis.
This is not current, I don't think. The 2014 GMAT does assume you know a number of things about parabolas, specifically:
1) The impact of the a coefficient (what happens if it's negative, what happen if it's positive)
2) The impact of the discriminant (specifically its relationship to the y-intercepts)
3) The relationship between the roots of a quadratic and the intercepts of a parabola
and there may be other expectations as well.
Hey Matt,
My point was more about whether or not we need to know how to find the equation of a parabola. That said, I consider point #3 relating more to finding the roots of an equation/x-intercepts than knowing how the graph of the parabola looks (although the concepts are linked).
As for point #2, I'm not sure what you mean by the relationship between the discriminant and the y-intercept. For any quadratic in the form y = ax² + bx + c, the y-intercept will be at (0, c). If you're referring to the x-intercept (and not the y-intercept), then points #2 and #3 are kind of the same and can be handled without knowing a great deal about how the parabola actually looks.
I'd be surprised to learn that test-takers are required to know how the a coefficient impacts the graph of a parabola, other than
perhaps whether a is negative or positive (in which case students can just as easily easily plot a few points to see the effect). IF that is required knowledge, I'd say that's as far as the test-takers would go. That is, I don't believe we're required to know how the
magnitude of a (i.e., y = 2x² - 3x + 1 vs y = x² - 3x + 1) affects the parabola.
Cheers,
Brent
