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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.

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.

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

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.