Find the real zeros of the function algebraically

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In summary, the given expression, f(x)=x^3+5x^2+9x+45, can be factored into (x^2+9)(x+5)=0 by factoring out the greatest common factor of x+5. This is similar to factoring a monomial in a polynomial expression.
  • #1
swatmedic05
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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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  • #2
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?
 
  • #3
[tex]\begin{aligned}
x^3 + 5x^2 + 9x + 45 &= 0 \\
x^2(x + 5) + 9(x + 5) &= 0 \\
(x^2 + 9)(x + 5) &= 0
\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
 
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  • #4
eumyang said:
[tex]\begin{aligned}
x^3 + 5x^2 + 9x + 45 &= 0 \\
x^2(x + 5) + 9(x + 5) &= 0 \\
(x^2 + 9)(x + 5) &= 0
\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
 
  • #5
Fixed. Didn't mean to use the term "monomial" -- just GCF. This is what you get for replying at 5am. :P69
 

FAQ: Find the real zeros of the function algebraically

How do I find the real zeros of a function algebraically?

To find the real zeros of a function algebraically, you can set the function equal to zero and then solve for the variable using techniques such as factoring, the quadratic formula, or the rational root theorem.

What are real zeros of a function?

Real zeros of a function are the values of the variable that make the function equal to zero. In other words, they are the x-values where the graph of the function crosses the x-axis.

Can a function have more than one real zero?

Yes, a function can have multiple real zeros. For example, a quadratic function can have two real zeros, while a cubic function can have three real zeros.

How can I check if my calculated zeros are correct?

You can check if your calculated zeros are correct by plugging them back into the original function and seeing if the result is equal to zero. Additionally, you can graph the function and see if the calculated zeros align with the x-intercepts.

Are there any shortcuts or tricks for finding real zeros of a function?

There are a few shortcuts or tricks for finding real zeros of a function, such as using the graphing calculator to approximate the zeros or using the Descartes' Rule of Signs to estimate the number of real zeros. However, these techniques should not replace the algebraic methods for finding the exact real zeros.

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