So, at least one of the factors must equal 0. If x + 1 = 0, then x = −1. If x + 3 = 0, then x = −3. Since −1 is
(B), that’s the one you want.
In addition to your knowing how to solve easily factorable quadratics, the test writers would also like to
see you demonstrate your understanding of the quadratic formula. I know what you are thinking: “Not that
thing AGAIN! Can’t I just solve it with that nifty program I have on my graphing calculator?” Why yes,
yes you can, but only if the problem appears in the calculator-permitted section of the test. Trust us on this
one—the test writers are not always going to put these types of problems in the calculator section.
Knowing the quadratic formula is an easy way to gain points on a question the test writers intend to be
“hard.”
For a quadratic equation in the form y = ax^2 + bx + c, the quadratic formula is:x = To find the roots of a quadratic, or the points where y = 0, simply plug your values for a, b, and c into the
quadratic formula.
The Signs They
Are a Changin’
The quadratic formula
works for quadratics in
the form y = ax^2 + bx + c.
There is only addition in
that form, so be careful
when your quadratic has
negative signs in it.Here’s an example:
7 x^2 – 5x − 17 = 0So a = 7, b = –5, and c = –17. Plugging the constants into the quadratic equation you get