GMAT Question of the Day - Daily to your Mailbox; hard ones only

It is currently 17 Jan 2019, 17:28

Close

GMAT Club Daily Prep

Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track
Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

Close

Request Expert Reply

Confirm Cancel
Events & Promotions in January
PrevNext
SuMoTuWeThFrSa
303112345
6789101112
13141516171819
20212223242526
272829303112
Open Detailed Calendar
  • The winning strategy for a high GRE score

     January 17, 2019

     January 17, 2019

     08:00 AM PST

     09:00 AM PST

    Learn the winning strategy for a high GRE score — what do people who reach a high score do differently? We're going to share insights, tips and strategies from data we've collected from over 50,000 students who used examPAL.
  • Free GMAT Strategy Webinar

     January 19, 2019

     January 19, 2019

     07:00 AM PST

     09:00 AM PST

    Aiming to score 760+? Attend this FREE session to learn how to Define your GMAT Strategy, Create your Study Plan and Master the Core Skills to excel on the GMAT.

If a and b are constants, and the equation [m]x^3 +ax^2 +bx = 64[/m] h

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:

Hide Tags

 
Senior DS Moderator
User avatar
V
Joined: 27 Oct 2017
Posts: 1195
Location: India
Concentration: International Business, General Management
GPA: 3.64
WE: Business Development (Energy and Utilities)
Premium Member CAT Tests
If a and b are constants, and the equation [m]x^3 +ax^2 +bx = 64[/m] h  [#permalink]

Show Tags

New post 27 Oct 2018, 09:27
1
00:00
A
B
C
D
E

Difficulty:

  45% (medium)

Question Stats:

53% (01:13) correct 47% (01:48) wrong based on 27 sessions

HideShow timer Statistics

If a and b are constants, and the equation \(x^3 +ax^2 +bx = 64\) has precisely one solution for x, what is the value of b?
A) 48
B) 16
C) 24
D) -16
E) -67

Weekly Quant Quiz #6 Question No 9


_________________

Win GMAT CLUB Test- Weekly Quant Quiz Contest
Weekly Quant Quiz Questions- Direct Download
SC: Confusable words

All you need for Quant, GMAT PS Question Directory,GMAT DS Question Directory
Error log/Key Concepts
Combination Concept: Division into groups
Question of the Day (QOTD)
Free GMAT CATS

Senior DS Moderator
User avatar
V
Joined: 27 Oct 2017
Posts: 1195
Location: India
Concentration: International Business, General Management
GPA: 3.64
WE: Business Development (Energy and Utilities)
Premium Member CAT Tests
Re: If a and b are constants, and the equation [m]x^3 +ax^2 +bx = 64[/m] h  [#permalink]

Show Tags

New post 27 Oct 2018, 09:27
1
Because if this cubic polynomial has only one root, 4 , then the equation can be written as:

(x - 4)^3 = 0

And then when we expand this we will get :

\(x^3 - 3*4*x^2 + 3*4^2*x - 64 = 0\)

Hence comparing to equation given, we get b = 48
_________________

Win GMAT CLUB Test- Weekly Quant Quiz Contest
Weekly Quant Quiz Questions- Direct Download
SC: Confusable words

All you need for Quant, GMAT PS Question Directory,GMAT DS Question Directory
Error log/Key Concepts
Combination Concept: Division into groups
Question of the Day (QOTD)
Free GMAT CATS

Intern
Intern
avatar
B
Joined: 26 Mar 2018
Posts: 1
Re: If a and b are constants, and the equation [m]x^3 +ax^2 +bx = 64[/m] h  [#permalink]

Show Tags

New post 27 Oct 2018, 22:47
x=4. using sum of multiplication of roots b=48
Manager
Manager
avatar
G
Joined: 14 Jun 2018
Posts: 223
Re: If a and b are constants, and the equation [m]x^3 +ax^2 +bx = 64[/m] h  [#permalink]

Show Tags

New post 27 Oct 2018, 23:31
\(x^3+ax^2+bx-64 = 0\)
let the root = k
product of roots = -(-64)/1 = 64
since the roots are the same , \(k^3 = 64 ; k = 4\)

sum of root = -a/1
a = -12

putting the value of x in the equation ,
64 + 16a + 4b = 64
16a+4b = 0
4a + b = 0
b = -4a = 48
Intern
Intern
avatar
B
Joined: 21 Aug 2018
Posts: 3
Re: If a and b are constants, and the equation [m]x^3 +ax^2 +bx = 64[/m] h  [#permalink]

Show Tags

New post 28 Oct 2018, 02:47
I got A for the answer.

x3+ax2+bx=64
<=> x^3 + ax^2 + bx - 64 = 0

Vieta's theorem
x1*x2*x3 = -(-64)/1

Since there is only 1 value of x (x1, x2 and x3 are the same), meaning x^3 = 64 => x=4

x1x2 +x2x3 + x3x1 = b/1
or 4*4 + 4*4 +4 *4 = 16 + 16 + 16 = 48
GMAT Club Bot
Re: If a and b are constants, and the equation [m]x^3 +ax^2 +bx = 64[/m] h &nbs [#permalink] 28 Oct 2018, 02:47
Display posts from previous: Sort by

If a and b are constants, and the equation [m]x^3 +ax^2 +bx = 64[/m] h

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  


Copyright

GMAT Club MBA Forum Home| About| Terms and Conditions and Privacy Policy| GMAT Club Rules| Contact| Sitemap

Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne

Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.