quadratic formula

Here are some cases where the quadratic formula can be useful on the GMAT:

1) Let's say you have the following quadratic: 2x^2+5x-33=0, this particular quadratic came up as part of an official GMAT problem. This can be solved by factoring and that is what I would recommend. However, if you get stuck or cannot do it for any reason, then you can always resort to the quadratic formula(that is some work too), but at least you will have your answer. So the first use is as a backup for solving quadratic equations.

2) On some of the hard GMAT problems you may be tested on being able to apply the concepts based on the quadratic formula. This is only applicable to students targeting 90th percentile plus on the quant. I have seen a few Official GMAT questions in the actual GMAT exam that requires one to know how b^2 - 4ac impacts the nature of the roots and how it relates to whether a parabola intersects the x-axis or not. There are also others that have relied on students knowing how the sum and product of the roots are related to the coefficients of the general quadratic equation ax^2+bx+c=0.

In a nutshell if you are targeting a 90 percentile plus score make sure you fully understand the quadratic formula and how it relates to the roots and intersections of the corresponding parabola.

Cheers,
Dabral