Chapter 3: Problem 8
Given that \(x+\frac{2}{3}\) is a factor of the function \(f(x)=3 x^{4}+2 x^{3}-36 x^{2}+24 x+32\) factorize \(f\) completely.
Short Answer
Expert verified
The complete factorization is \((3x+2)(x-2)(3x-2)(x+4)\).
Step by step solution
01
Recognize the Given Factor
The function is given as \( f(x) = 3x^4 + 2x^3 - 36x^2 + 24x + 32 \). We know that \( x + \frac{2}{3} \) is a factor, which we can rewrite as \( 3x + 2 \) for easier polynomial division.
02
Perform Synthetic Division
To factor the polynomial, start by dividing \( f(x) \) by \( 3x + 2 \) using synthetic division. Set up the division by using the root of \( 3x + 2 = 0 \); that is \( x = -\frac{2}{3} \). Using coefficients: \( 3, 2, -36, 24, 32 \), perform the division. Check that the remainder is 0 and take note of the quotient which will be \( 3x^3 - 2x^2 - 34x + 16 \).
03
Further Factorize the Quotient
Now, factor the cubic polynomial \( 3x^3 - 2x^2 - 34x + 16 \). Check for possible rational roots using the Rational Root Theorem. Testing potential roots simplifies the cubic polynomial to factor as \((x - 2)(3x^2 + 4x - 8)\).
04
Factor the Quadratic Portion
Next, factor the quadratic \(3x^2 + 4x - 8\). Use the quadratic formula: \[ x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} \], where \( a=3, b=4, c=-8 \). This gives us the roots \[ x = \frac{-4 \pm 8}{6} \], which further factorizes to \( (3x - 2)(x + 4) \).
05
Write the Complete Factorization
Combine the factors from the steps above to write the complete factorization of \( f(x) \). The complete factorization is: \((3x + 2)(x - 2)(3x - 2)(x + 4)\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Synthetic Division
Synthetic division is a simplified form of dividing a polynomial by a binomial of the form \(x - c\). It is quicker and less cumbersome than long division. Here's how it works:
- Identify the coefficients of the polynomial you are dividing.
- Use the root of the divisor. For example, if you are dividing by \(3x + 2\), solve \(3x + 2 = 0\) to find \(x = -\frac{2}{3}\).
- List the coefficients: \(3, 2, -36, 24, 32\).
- Perform the synthetic division by using these coefficients and the divisor root.
- Multiply the root by the first coefficient and add it to the next.
- Repeat the process for all coefficients.
- The last number is the remainder. If it’s 0, you have factored correctly.
Rational Root Theorem
The Rational Root Theorem helps in finding the possible rational roots of a polynomial equation. This theorem suggests that if a polynomial has a rational root \(\frac{p}{q}\), then \(p\) is a factor of the constant term and \(q\) is a factor of the leading coefficient. For example, consider the polynomial \(3x^{3} - 2x^{2} - 34x + 16\):
- The constant term is 16, and its factors are \(\pm 1, \pm 2, \pm 4, \pm 8, \pm 16\).
- The leading coefficient is 3, and its factors are \(\pm 1, \pm 3\).
Quadratic Formula
When a polynomial expression reduces to a quadratic polynomial, the quadratic formula is an essential tool for factorization. The quadratic formula is:\[ x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} \]Where \(a\), \(b\), and \(c\) are coefficients from the quadratic expression \(ax^2 + bx + c\). This formula finds the roots of the quadratic equation, which are the values of \(x\) where the polynomial equals zero.In the given exercise, the quadratic \(3x^2 + 4x - 8\) was solved using the quadratic formula:
- \(a = 3, b = 4, c = -8\)
- Plugging into the formula yields roots \(x = \frac{-4 \pm 8}{6}\).
Polynomial Division
Polynomial division, both synthetic and long division, is used to divide polynomials when factorizing or simplifying expressions. It operates much like arithmetic long division.For a division \(\frac{f(x)}{d(x)}\):
- The polynomial \(f(x)\) is divided by a simpler polynomial \(d(x)\).
- Long division results in a quotient and sometimes a remainder.
- We divide the leading terms, multiply and subtract successively just as we do with numbers.
- Repeat for each descending power of the polynomial.