Live GMAT classes with Target Test Prep start Nov 21 and Nov 22. First class free.

See classes
Target Test Prep · GMAT

Choose how you want to prepare

Learn live with an expert or move at your own pace. Every option includes the complete TTP study system.

Newsweek Readers’ Choice Awards 2026 winner: Target Test Prep, #1 Test Prep

Target Test Prep was voted #1 Best Test Prep in the 2026 Newsweek Readers’ Choice™ Awards.

★★★★★5.0563 reviews
GMATLiveTeachStarts Nov 22
Josh Braslow, Target Test Prep GMAT expert
LIVE ONLINE CLASSES

Get Ready for GMAT Test Day Faster with Live Online Classes

with Josh Braslow, 20+ years in test prep

Nov 22 · Josh Braslow
Sun · 9:30 AM to 12:30 PM ET
Included
40 hours of live online classes + 6 months of TTP OnDemand
  • Attend the first class for free
  • Every class is recorded, so you never fall behind
View classes & enroll
Limited seats availableTarget Test Prep
EALiveTeachOnDemandStart anytime
EXECUTIVE ASSESSMENT

Target Test Prep EA OnDemand

Self-paced EA prep. Study on your schedule.

EXECUTIVE ASSESSMENT

with

165+ EA score guarantee
$05-day trial no automatic billing
Schedule
Included
40 hours of live online classes plus six months of access to the complete TTP EA OnDemand course.
  • 165+ EA Score Guarantee
  • 4,100+ Quant, Verbal, and Integrated Reasoning practice questions
  • 400+ hours of in-depth video lessons
  • 3,000+ step-by-step video solutions
View EA class & enroll Start free 5-day trial
Limited cohort · enrollment openTrial includes full course accessTarget Test Prep
GMATOnDemandStart anytime
SELF-PACED MASTERCLASS

Target Test Prep GMAT OnDemand

Complete access from day one. Study on your schedule.

715+ score guarantee
$0to start then $127/mo
  • Personalized study plan and analytics
  • Thousands of lessons and practice questions
Start free 5-day trial
Read 563 reviewsTarget Test Prep

Quadratic Equation question

Problem Solving — algebra and arithmetic
Expert replies
Post new topic Post Reply
Subscribe topic
Previous Topic Next Topic
Junior | Next Rank: 30 Posts
Posts: 24
Joined: Sat Dec 13, 2008 6:12 pm
Location: chicago
by gxj007 » Sun Dec 14, 2008 11:28 am
How do you solve a quadratic equation if there are not numbers which multiply to the last number and add to the middle number?

ie:

x^2 - 2x - 8 = 0

or x^2 - 2x - 7 =0

I know that if you have someting like x^2 - 2x - 3 = 0 you can factor it to
x-3 and x+1 but how about the cases above?

thanks!
Top
Join the discussion
Source: — Quantitative Reasoning |

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 16206
Joined: Mon Dec 08, 2008 6:26 pmFollowed by: 1268 members
Location: Vancouver, BC
Thanked: 5254 times
GMAT Score:770

by Brent@GMATPrepNow » Sun Dec 14, 2008 3:19 pm
The "official" answer would be to use the quadratic formula, which is far too awful to try to type here. Google "quadratic formula" to learn more.

GMAC includes the quadratic formula in its curriculum but, to date, I have not seen one single official GMAT question that requires the quadratic formula. I do know one instructor who says a former student claims to have had a question that required the quadratic formula, but I'll believe it when I see it. If you ask me, it sounds like an urban myth :D

The whole quadratic formula thing is a bit of a paradox in that, if you were to see a question requiring this formula, then you are probably scoring in the 750+ range, in which case you probably already know the formula. If you are not scoring in the 750+ range, then you won't see questions requiring the formula so don't waste your time memorizing it. Of course, all of this assumes that there are such questions.

Are there any other GMAT instructors out there who would like to weigh in on this? Am I missing anything?
Top
Join the discussion
User avatar
Legendary Member
Posts: 2134
Joined: Mon Oct 20, 2008 11:26 pmFollowed by: 25 members
Thanked: 237 times
GMAT Score:730

Re: Quadratic Equation question

by logitech » Sun Dec 14, 2008 4:03 pm
gxj007 wrote:How do you solve a quadratic equation if there are not numbers which multiply to the last number and add to the middle number?

ie:

x^2 - 2x - 8 = 0

or x^2 - 2x - 7 =0

I know that if you have someting like x^2 - 2x - 3 = 0 you can factor it to
x-3 and x+1 but how about the cases above?

thanks!
for example

x^2 - 2x - 8 = 0

AX^2+BX+C=0

easy method

you have to find the factors of both A and C and try to get B as below:

A = A1xA2
C=C1xC2

And B must be equal to:

B= A1xC2 + A2XC1

lets apply this to:

x^2 - 2x - 8 = 0

1x -4
1x +2

(2x + (-4x) = -2x ( remember B =-2)

so

x^2 - 2x - 8 = 0

(x-4)(x+2)=0
LGTCH
---------------------
"DON'T LET ANYONE STEAL YOUR DREAM!"
Top
Join the discussion

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 16206
Joined: Mon Dec 08, 2008 6:26 pmFollowed by: 1268 members
Location: Vancouver, BC
Thanked: 5254 times
GMAT Score:770

by Brent@GMATPrepNow » Sun Dec 14, 2008 4:20 pm
Oops, I didn't even notice that the first equation (x^2 - 2x - 8 = 0 ) is factorable.

What about the second equation (x^2 - 2x - 7 =0) ?
Any thoughts about the quadtatic formula?

Do any instructors out there delve deeply into this formula?

I'm quite curious.
Top
Join the discussion
User avatar
Legendary Member
Posts: 2134
Joined: Mon Oct 20, 2008 11:26 pmFollowed by: 25 members
Thanked: 237 times
GMAT Score:730

by logitech » Sun Dec 14, 2008 4:31 pm
Brent Hanneson wrote:Oops, I didn't even notice that the first equation (x^2 - 2x - 8 = 0 ) is factorable.

What about the second equation (x^2 - 2x - 7 =0) ?
Any thoughts about the quadtatic formula?

Do any instructors out there delve deeply into this formula?

I'm quite curious.
The Quadratic Formula is out of GMAT's scope BUT it does not hurt to learn it..
You do not have the required permissions to view the files attached to this post.
LGTCH
---------------------
"DON'T LET ANYONE STEAL YOUR DREAM!"
Top
Join the discussion
Junior | Next Rank: 30 Posts
Posts: 24
Joined: Sat Dec 13, 2008 6:12 pm
Location: chicago

by gxj007 » Mon Dec 15, 2008 9:36 am
Thanks for your responses. So is it safe to say that the strategy for completing the square is probably out of scope as well? I guess I just want to ensure that I'm not wasting time going too far in depth with certain concepts if they won't even show up on the test.

thanks again!
Top
Join the discussion
User avatar
Legendary Member
Posts: 2134
Joined: Mon Oct 20, 2008 11:26 pmFollowed by: 25 members
Thanked: 237 times
GMAT Score:730

by logitech » Mon Dec 15, 2008 10:06 am
gxj007 wrote:Thanks for your responses. So is it safe to say that the strategy for completing the square is probably out of scope as well? I guess I just want to ensure that I'm not wasting time going too far in depth with certain concepts if they won't even show up on the test.

thanks again!
Old greek saying:

Eat the grape, and don't ask where it s coming from.

Just learn the formula and use it when you need it.

Good luck!
LGTCH
---------------------
"DON'T LET ANYONE STEAL YOUR DREAM!"
Top
Join the discussion