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

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

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07 Jan 2008, 21:07
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

5x^2 + 3x -2 = 7x

why does this have just one solution?

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SVP
Joined: 04 May 2006
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07 Jan 2008, 21:19
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
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Director
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07 Jan 2008, 23:43
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.

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Manager
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08 Jan 2008, 11:04
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!!!???

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Manager
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08 Jan 2008, 11:42
can some one explain the answer?

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CEO
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08 Jan 2008, 11:44
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?
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Manager
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09 Jan 2008, 00:32
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

Kudos [?]: 63 [0], given: 2

CEO
Joined: 17 Nov 2007
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Kudos [?]: 4661 [0], given: 360

Concentration: Entrepreneurship, Other
Schools: Chicago (Booth) - Class of 2011
GMAT 1: 750 Q50 V40

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09 Jan 2008, 00:46
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.
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Director
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09 Jan 2008, 01:53
Can you please post the entire question? Thanks.

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09 Jan 2008, 21:21
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.

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Re: sorry, basic question   [#permalink] 09 Jan 2008, 21:21
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