Find all School-related info fast with the new School-Specific MBA Forum

 It is currently 03 May 2015, 14:59

### 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

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

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

# 5x^2 + 3x -2 = 7x why does this have just one solution

Author Message
TAGS:
Manager
Joined: 15 Nov 2007
Posts: 135
Followers: 1

Kudos [?]: 30 [0], given: 2

5x^2 + 3x -2 = 7x why does this have just one solution [#permalink]  07 Jan 2008, 20:07
5x^2 + 3x -2 = 7x

why does this have just one solution?
SVP
Joined: 04 May 2006
Posts: 1936
Schools: CBS, Kellogg
Followers: 19

Kudos [?]: 441 [0], given: 1

Re: sorry, basic question [#permalink]  07 Jan 2008, 20:19
dominion wrote:
5x^2 + 3x -2 = 7x

why does this have just one solution?

I draw f(x)=7x and f(x)=5x^2+3x-2 and find that there is only one intersect btw them

Anyway, if I first see this equation on gmat, maybe I will also fall in the trap
_________________
Director
Joined: 09 Aug 2006
Posts: 766
Followers: 1

Kudos [?]: 69 [0], given: 0

Re: sorry, basic question [#permalink]  07 Jan 2008, 22:43
dominion wrote:
5x^2 + 3x -2 = 7x

why does this have just one solution?

Where did u get this from?

5x^2 - 4x - 2 = 0

How do u solve this for x? 2*5 = 10. How do you factor 10 so that the sum of factors is 4? I don't want to use the special formula since that's outside the scope of GMAT.
Manager
Joined: 15 Nov 2007
Posts: 135
Followers: 1

Kudos [?]: 30 [0], given: 2

Re: sorry, basic question [#permalink]  08 Jan 2008, 10:04
GK_Gmat wrote:
dominion wrote:
5x^2 + 3x -2 = 7x

why does this have just one solution?

Where did u get this from?

5x^2 - 4x - 2 = 0

How do u solve this for x? 2*5 = 10. How do you factor 10 so that the sum of factors is 4? I don't want to use the special formula since that's outside the scope of GMAT.

it's in the official GMAT preparation software...

WALKER!!!???
Manager
Joined: 04 Jan 2008
Posts: 85
Followers: 1

Kudos [?]: 10 [0], given: 0

Re: sorry, basic question [#permalink]  08 Jan 2008, 10:42
can some one explain the answer?
CEO
Joined: 17 Nov 2007
Posts: 3578
Concentration: Entrepreneurship, Other
Schools: Chicago (Booth) - Class of 2011
GMAT 1: 750 Q50 V40
Followers: 406

Kudos [?]: 2140 [0], given: 359

Re: sorry, basic question [#permalink]  08 Jan 2008, 10:44
Expert's post
dominion wrote:
WALKER!!!???

5x² + 3x -2 = 7x
5x²-4x-2=0
D=4²+4*5*2=56>0

There are two solutions.
can you post entire question?
_________________

HOT! GMAT TOOLKIT 2 (iOS) / GMAT TOOLKIT (Android) - The OFFICIAL GMAT CLUB PREP APP, a must-have app especially if you aim at 700+ | PrepGame

Manager
Joined: 01 Jan 2008
Posts: 227
Schools: Booth, Stern, Haas
Followers: 1

Kudos [?]: 48 [0], given: 2

Re: sorry, basic question [#permalink]  08 Jan 2008, 23:32
sondenso wrote:
dominion wrote:
5x^2 + 3x -2 = 7x

why does this have just one solution?

I draw f(x)=7x and f(x)=5x^2+3x-2 and find that there is only one intersect btw them

Anyway, if I first see this equation on gmat, maybe I will also fall in the trap

I think tangent point and intersection point are different things so either this point is tangent point rather than intersection (line of 7x and starting point of parabola's branches) or they intersect at two points...imo
CEO
Joined: 17 Nov 2007
Posts: 3578
Concentration: Entrepreneurship, Other
Schools: Chicago (Booth) - Class of 2011
GMAT 1: 750 Q50 V40
Followers: 406

Kudos [?]: 2140 [0], given: 359

Re: sorry, basic question [#permalink]  08 Jan 2008, 23:46
Expert's post
sondenso wrote:
I draw f(x)=7x and f(x)=5x^2+3x-2 and find that there is only one intersect btw them
Anyway, if I first see this equation on gmat, maybe I will also fall in the trap

If we draw carefully f(x)=7x and f(x)=5x^2+3x-2 they have two intersection points.
_________________

HOT! GMAT TOOLKIT 2 (iOS) / GMAT TOOLKIT (Android) - The OFFICIAL GMAT CLUB PREP APP, a must-have app especially if you aim at 700+ | PrepGame

Director
Joined: 09 Aug 2006
Posts: 766
Followers: 1

Kudos [?]: 69 [0], given: 0

Re: sorry, basic question [#permalink]  09 Jan 2008, 00:53
Can you please post the entire question? Thanks.
CEO
Joined: 29 Mar 2007
Posts: 2591
Followers: 16

Kudos [?]: 234 [0], given: 0

Re: sorry, basic question [#permalink]  09 Jan 2008, 20:21
dominion wrote:
5x^2 + 3x -2 = 7x

why does this have just one solution?

owell time for the ol quad equation x=(-b+/-sqrtb^2-4ac)/2a

x^2-4x/5 -2/5=0

a=1 b=-4/5 c=-2/5

x= (4/5+/-sqrt16/25+8/5)/2 --> (4/5 +/- sqrt(56/25))/2)

seems like we have two solutions that im not going to go any further to solve.
Re: sorry, basic question   [#permalink] 09 Jan 2008, 20:21
Similar topics Replies Last post
Similar
Topics:
If 4 is one solution of the equation x^2 + 3x + k = 10 3 06 May 2012, 08:38
What is the ratio of x to y? (1) 5x = 2y (2) 2y = 7x 8 8 21 Jun 2011, 17:51
2 If x(x - 5)(x + 2) = 0, is x negative? (1) x2 7x 0 (2) x2 2x 1 16 Aug 2009, 22:17
1 If x(x-5)(x+2) = 0, is x negative? (1) x^2 - 7x does not 6 12 Jul 2008, 06:32
If x(x - 5)(x + 2) = 0, is x negative? (1) x2 7x ? 0 1 22 Jul 2007, 20:17
Display posts from previous: Sort by