ps - quadratic root q - The Beat The GMAT Forum - Expert GMAT Help & MBA Admissions Advice

ps - quadratic root q

Expert replies

ccassel: Master | Next Rank: 500 Posts; Posts: 118; Joined: Wed Mar 16, 2011 1:44 pmFollowed by: 2 members; Location: Canada; GMAT Score:530

by ccassel » Mon Apr 18, 2011 5:54 pm

How would you explain the answer to this question?

If one root of the equation 2x^2+3x-k=0 is 6, what is the value of k?

A. 90
B. 42
C. 18
D. 10
E. -10

Answer is A

Like this post

Source: Beat The GMAT — Problem Solving | Mon Apr 18, 2011 5:54 pm

vineeshp: Legendary Member; Posts: 965; Joined: Thu Jan 28, 2010 12:52 amFollowed by: 34 members; Thanked: 156 times; GMAT Score:720

by vineeshp » Mon Apr 18, 2011 6:04 pm

If 6 is the root of the equation with variable x, it means x can take the value 6.

That is,
2x^2+3x-k=0
Substituting 6 for x,

2*6^2+3*6-k=0

72 + 18 -k =0

k =90

Vineesh,
Just telling you what I know and think. I am not the expert.

Like this post

GMAT/MBA Expert

Anurag@Gurome: GMAT Instructor; Posts: 3835; Joined: Fri Apr 02, 2010 10:00 pmFollowed by: 523 members; Location: Milpitas, CA; Thanked: 1854 times; GMAT Score:770

by Anurag@Gurome » Mon Apr 18, 2011 7:52 pm

ccassel wrote:How would you explain the answer to this question?

If one root of the equation 2x^2+3x-k=0 is 6, what is the value of k?

A. 90
B. 42
C. 18
D. 10
E. -10

Answer is A

Since one of the roots is 6, so it will satisfy the given quadratic equation, 2xÂ² + 3x - k = 0
So, 2(6)Â² + 3(6) - k = 0 implies 90 - k = 0 or k = 90

The correct answer is A.

Anurag Mairal, Ph.D., MBA
GMAT Expert, Admissions and Career Guidance
Gurome, Inc.
1-800-566-4043 (USA)

Join Our Facebook Groups
GMAT with Gurome
https://www.facebook.com/groups/272466352793633/
Admissions with Gurome
https://www.facebook.com/groups/461459690536574/
Career Advising with Gurome
https://www.facebook.com/groups/360435787349781/

Like this post

manpsingh87: Master | Next Rank: 500 Posts; Posts: 436; Joined: Tue Feb 08, 2011 3:07 amFollowed by: 6 members; Thanked: 72 times

by manpsingh87 » Mon Apr 18, 2011 10:13 pm

ccassel wrote:How would you explain the answer to this question?

If one root of the equation 2x^2+3x-k=0 is 6, what is the value of k?

A. 90
B. 42
C. 18
D. 10
E. -10

Answer is A

f(x)=2x^2+3x-k; now if 6 is a factor of f(x) than f(x)=0; at x=6..!!!
therefore we have 2*36+28-k=0; k=90..!!

O Excellence... my search for you is on... you can be far.. but not beyond my reach!

Like this post

Post new topic Post Reply

• Page 1 of 1

GMAT Course Reviews

559 reviews

1168 reviews

431 reviews

359 reviews

147 reviews

5/5

5 Star (560 Reviews)

"Target Test Prep is the closest to the official version of the GMAT exam, about 99% accuracy in terms of the quality and quantity of information. The course has excellently created singular sets of focused lessons and tests for every possible topic that one could come across in the official GMAT exam."

"The TTP course maximizes the efficiency of the time you spend studying. It will take time and effort but I could almost guarantee that if you complete the course exactly as it is laid out you will get an amazing score. They also have a very responsive team willing to help with any questions you might have."

"TTP has two things that I think no other test prep company offers: A teaching approach that reinforces understanding and an attitude that will give you the mental preparedness needed to succeed on the test. TTP gives you a deep understanding of the concept you need to know while teaching you how to think."

Write a Review