Find the real zeros of the function algebraically

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Homework Help Overview

The discussion revolves around finding the real zeros of the polynomial function f(x) = x^3 + 5x^2 + 9x + 45 by factoring. Participants are examining the steps taken to factor the polynomial and the implications of those steps.

Discussion Character

  • Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants are exploring the factorization of the polynomial and questioning the treatment of the factor (x + 5). There is discussion about the greatest common factor (GCF) and its role in the factorization process.

Discussion Status

The conversation is focused on clarifying the factorization steps and addressing potential errors in terminology. Some participants are correcting each other regarding the classification of the GCF and discussing the implications of factoring out (x + 5).

Contextual Notes

There is mention of a possible typo in the factorization steps, and participants are reflecting on their understanding of the terminology used in the context of factoring polynomials.

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f(x)=x^3+5x^2+9x+45
x^3+5x^2+9x+45=0
x^2(x+5)+9(x-5)=0
(x^2+9)(x+5)=0
What happends to the (x+5)?
 
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swatmedic05 said:
f(x)=x^3+5x^2+9x+45
x^3+5x^2+9x+45=0
x^2(x+5)+9(x-5)=0
There's an error in the step above.
swatmedic05 said:
(x^2+9)(x+5)=0
What happends to the (x+5)?

Since (x2 + 9)(x + 5) = 0, then either x2 + 9 = 0 or x + 5 = 0. Can you continue from here?
 
[tex]\begin{aligned}<br /> x^3 + 5x^2 + 9x + 45 &= 0 \\<br /> x^2(x + 5) + 9(x + 5) &= 0 \\<br /> (x^2 + 9)(x + 5) &= 0<br /> \end{aligned}[/tex]
I'm assuming that the error pointed out above is just a typo, so I'll just fix it. As for
What happened to the (x+5)?
It was the greatest common factor, so it got factored out.

Say you wanted to factor 16x - 28. The GCF is 4, and you could rewrite the expression as
4(4x) - 4(7),
and then factor out the 4 to get
4(4x - 7).

It's the same thing in your problem. The GCF is an expression: x + 5. You factor the x + 5 out in [tex]x^2 \bold{(x + 5)} + 9 \bold{(x + 5)} = 0[/tex] and you get [tex](x^2 + 9)(x + 5) = 0[/tex]. Maybe part of the confusion is that the GCF appears last instead of first?69
 
Last edited:
eumyang said:
[tex]\begin{aligned}<br /> x^3 + 5x^2 + 9x + 45 &= 0 \\<br /> x^2(x + 5) + 9(x + 5) &= 0 \\<br /> (x^2 + 9)(x + 5) &= 0<br /> \end{aligned}[/tex]
I'm assuming that the error pointed out above is just a typo, so I'll just fix it. As for

It was the greatest common monomial factor, so it got factored out.
It was the greatest linear factor. It is not a monomial, it is a binomial, just like [itex]x^2+ 9[/itex].

Say you wanted to factor 16x - 28. The GCF is 4, and you could rewrite the expression as
4(4x) - 4(7),
and then factor out the 4 to get
4(4x - 7).

It's the same thing in your problem. The GCF is an expression: x + 5. You factor the x + 5 out in [tex]x^2 \bold{(x + 5)} + 9 \bold{(x + 5)} = 0[/tex] and you get [tex](x^2 + 9)(x + 5) = 0[/tex]. Maybe part of the confusion is that the GCF appears last instead of first?


69
 
Fixed. Didn't mean to use the term "monomial" -- just GCF. This is what you get for replying at 5am. :P69
 

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