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

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

why does this have just one solution?
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Re: sorry, basic question [#permalink] New post 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
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Re: sorry, basic question [#permalink] New post 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.
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Re: sorry, basic question [#permalink] New post 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!!!???
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Re: sorry, basic question [#permalink] New post 08 Jan 2008, 10:42
can some one explain the answer?
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Re: sorry, basic question [#permalink] New post 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?
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Re: sorry, basic question [#permalink] New post 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
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Re: sorry, basic question [#permalink] New post 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.
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Re: sorry, basic question [#permalink] New post 09 Jan 2008, 00:53
Can you please post the entire question? Thanks.
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Re: sorry, basic question [#permalink] New post 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
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