How can I factor a polynomial without using the rational root theorem?

In summary, to factor a polynomial like $6x^4+17x^3-24x^2-53x+30$ without using rational root theorem, one can use a combination of grouping and factoring by grouping. This involves breaking the polynomial into smaller, more manageable parts and factoring them separately. The final result can then be written as a product of these smaller factors. This method often involves some trial and error, but can be made easier by using tools such as Wolfram|Alpha.
  • #1
paulmdrdo1
385
0
I'm just curious as to how to go about factoring a polynomial like this one $6x^4+17x^3-24x^2-53x+30$ without using rational root theorem?

Thanks
 
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  • #2
You could write:

\(\displaystyle 6x^4+17x^3-24x^2-53x+30=\left(6x^4+12x^3\right)+\left(5x^3+10x^2\right)-\left(34x^2+68x\right)+\left(15x+30\right)=6x^3(x+2)+5x^2(x+2)-34x(x+2)+15(x+2)=(x+2)\left(6x^3+5x^2-34x+15\right)\)

\(\displaystyle 6x^3+5x^2-34x+15=\left(6x^3+18x^2\right)-\left(13x^2+39x\right)+\left(5x+15\right)=6x^2(x+3)-13x(x+3)+5(x+3)=(x+3)\left(6x^2-13x+5\right)\)

\(\displaystyle 6x^2-13x+5=(2x-1)(3x-5)\)

And so we have:

\(\displaystyle 6x^4+17x^3-24x^2-53x+30=(x+2)(x+3)(2x-1)(3x-5)\)
 
  • #3
MarkFL said:
You could write:

\(\displaystyle 6x^4+17x^3-24x^2-53x+30=\left(6x^4+12x^3\right)+\left(5x^3+10x^2\right)-\left(34x^2+68x\right)+\left(15x+30\right)=6x^3(x+2)+5x^2(x+2)-34x(x+2)+15(x+2)=(x+2)\left(6x^3+5x^2-34x+15\right)\)

\(\displaystyle 6x^3+5x^2-34x+15=\left(6x^3+18x^2\right)-\left(13x^2+39x\right)+\left(5x+15\right)=6x^2(x+3)-13x(x+3)+5(x+3)=(x+3)\left(6x^2-13x+5\right)\)

\(\displaystyle 6x^2-13x+5=(2x-1)(3x-5)\)

And so we have:

\(\displaystyle 6x^4+17x^3-24x^2-53x+30=(x+2)(x+3)(2x-1)(3x-5)\)

What technique did you use to determine the pair of numbers to be used to rewrite the expression? Was it by trial and error?
 
  • #4
paulmdrdo said:
What technique did you use to determine the pair of numbers to be used to rewrite the expression? Was it by trial and error?

Yes, there is generally guesswork involved in factoring polynomials. What I actually did was used W|A to factor it, and then constructed my post based on that. :D
 

FAQ: How can I factor a polynomial without using the rational root theorem?

What is a polynomial?

A polynomial is an algebraic expression that consists of variables and coefficients, combined using only the operations of addition, subtraction, and multiplication. Examples of polynomials include 2x^3 + 5x^2 - 3x + 1 and 4y^2 - 9.

What is the degree of a polynomial?

The degree of a polynomial is the highest exponent of the variable in the expression. For example, the polynomial 2x^3 + 5x^2 - 3x + 1 has a degree of 3, while the polynomial 4y^2 - 9 has a degree of 2.

What is the process of solving a polynomial equation?

The process of solving a polynomial equation, also known as finding the roots or zeros of a polynomial, involves determining the values of the variable that make the equation true. This can be done by factoring the polynomial, using the quadratic formula, or using other methods such as the rational root theorem.

Why is it important to find the roots of a polynomial?

Finding the roots of a polynomial is important because it allows us to determine the solutions to the equation. These solutions can be used to solve real-world problems, to graph the polynomial, or to simplify the expression.

What is the fundamental theorem of algebra?

The fundamental theorem of algebra states that every polynomial equation with complex coefficients has at least one complex root. This means that for every polynomial of degree n, there are exactly n complex roots. Additionally, the theorem states that every polynomial can be factored into linear and quadratic terms.

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