You probably remember FOIL (First Outer Inner Last) from high school and you may also remember how to find the roots of an equation. On the GRE, there are really only three quadric equation formats that you will see.
Memorize these equations:
(x + y)2 = x2 + 2xy + y2
(x – y)2 = x2 – 2xy + y2
(x + y)(x – y) = x2 – y2
Each of the above expressions has two states—the factored state and the squared state. When you see an expression in one state, rewrite it in the other state. Typically these questions will be about manipulating equations, not about solving for x. If the equations don’t match one of these three formats, see if you can factor numbers or variables out of them until they do.
Naturally, the minute you see a quadratic equation, either on a quantitative comparison or a problem-solving question, if you see variables in the question and variables in the answer choices, you can always Plug In. Use your Plug In set-up for Quant Comp and plug in more than once. On problem-solving questions make sure you have labeled the terms, circled a target number, and checked all of the answer choices.
For more practice and a more in-depth look at The Princeton Review math techniques, check out our student-friendly guidebook, Cracking the GRE.