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vanam52923
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vanam52923
I am bit confused with quadratic equation.please help Bunuel Kinshook @e-GmatQuant nick1816
VeritasKarishma
if the roots of equation quadratic equation are -1 and 3
so we can write it in the form (x+1)(x-3)=0

Also, we know x^2-sum of roots *x+product of roots=0

x^2 -(2)x-3=0

This is all correct!

Quote:
Now my question is
if it is given -1 and 3 are roots of ax^2 + bx + c=0
can we write it as (x+1)(x-3)=0
or will it be a(x+1)(x-3)=0,if this then how?

It's the second one. In order to rewrite a quadratic equation like (x + 1)(x - 3) = 0, the 'a' term has to be 1. In general, you can't be sure that ax^2 + bx + c equals (x + 1)(x - 3) exactly, unless you know that a = 1. Otherwise, given that the roots are -1 and 3, ax^2 + bx + c will be a multiple of (x + 1)(x - 3).

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Here the questioin which confused me was :

y= ax^2 + bx + c
The equation above represents a parabola in the XY-plane. If a < 0 and the x-intercepts of the parabola are – 1 and 3, which of the following could be the vertex of the parabola?

I'd be curious to see the answer choices.

Here's all you really know from the information provided:
- The vertex will be halfway between the two x-intercepts, because a parabola is symmetrical. So, the x coordinate of the vertex will be 1.
- Because a < 0, the parabola will open downwards, rather than upwards. (That's because the entire parabola is being multiplied by a negative value.) So, the vertex should have a positive y coordinate.

I hope that only one of the answer choices had an x coordinate of 1, and a y coordinate greater than 0!
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