How to find the zeros?

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September 14th 2009, 06:14 PM
nascar77

How to find the zeros?

Im having trouble finding the zeros of this polynomial:

-x^2+2x+4

I have tried factoring it and it dosent work i have tried the quadratic formula too but no luck. I am supposed to graph this but I need the zeros first. Anyone have any suggestions im really lost. Thanks for your help in advance.

PS. The first term is read as "negative x squared" im not sure how to do the symbols...
September 14th 2009, 06:23 PM
skeeter

Quote:

Originally Posted by nascar77

Im having trouble finding the zeros of this polynomial:

-x^2+2x+4

I have tried factoring it and it dosent work i have tried the quadratic formula too but no luck. I am supposed to graph this but I need the zeros first. Anyone have any suggestions im really lost. Thanks for your help in advance.

PS. The first term is read as "negative x squared" im not sure how to do the symbols...

$-x^2+2x+4 = 0$

$a = -1$

$b = 2$

$c = 4$

$x = \frac{-2 \pm \sqrt{2^2 - 4(-1)(4)}}{2(-1)}$

now ... what exactly is your problem in evaluating the above expression that uses the quadratic formula?
September 14th 2009, 06:37 PM
nascar77

Because the quadratic formula produces zeros that have imaginary numbers. But im actually supposed to graph this on a coordinate plane. The original funcion was f(x)=-x^3+4x^2-8. From here i used synthetic division and found one zero to be two. The quadratic i posted was the quotient left from the division.
September 14th 2009, 06:45 PM
skeeter

Quote:

Because the quadratic formula produces zeros that have imaginary numbers.

is that so?

$x = \frac{-2 \pm \sqrt{2^2 - 4(-1)(4)}}{2(-1)}$

$x = \frac{-2 \pm \sqrt{4 - (-16)}}{-2}$

$x = \frac{-2 \pm \sqrt{20}}{-2}$

$x = \frac{-2 \pm 2\sqrt{5}}{-2}$

$x = 1 \mp \sqrt{5}$

I'd say that x has two real zeros.
September 14th 2009, 06:52 PM
nascar77

I feel stupid I must have gotten lost somewhere in the algebra. thanks so much for your help!

-Kimberly