Chapter 3: Problem 34
Find all rational zeros of the polynomial, and write the polynomial in factored form. $$P(x)=2 x^{3}-3 x^{2}-2 x+3$$
Short Answer
Expert verified
The rational zeros are 1, \( \frac{3}{2} \), and -1, and the factored form is \( 2(x-1)(2x-3)(x+1) \).
Step by step solution
01
Identify Possible Rational Zeros
According to the Rational Root Theorem, the possible rational zeros of a polynomial are the factors of the constant term divided by the factors of the leading coefficient. For the polynomial \( P(x) = 2x^{3} - 3x^{2} - 2x + 3 \), the constant term is 3, and the leading coefficient is 2. Thus, the possible rational zeros are \( \pm 1, \pm 3, \pm \frac{1}{2}, \pm \frac{3}{2} \).
02
Evaluate Possible Zeros Using Synthetic Division
To find the actual rational zeros, we use synthetic division to test the possible zeros. We start with \( x = 1 \). Synthetic division of \( P(x) \) by \( x - 1 \) yields a remainder of 0, indicating that \( x = 1 \) is a zero. Repeat for \( x = -1 \), \( x = 3 \), etc. and find that \( x = \frac{3}{2} \) is another zero.
03
Factorize the Polynomial
With known zeros \( x = 1 \) and \( x = \frac{3}{2} \), we form the factors \( (x - 1) \) and \( (2x - 3) \). Given \( P(x) \) is a cubic polynomial, it will have three roots, which means it can be expressed as \( P(x) = 2(x-1)(2x-3)Q(x) \). Calculate \( Q(x) \) to find the remaining factorisation. By division, find \( Q(x) = (x + 1) \).
04
Write the Polynomial in Factored Form
Combining the factors found, the polynomial can be completely factored as \( P(x) = 2(x - 1)(2x - 3)(x + 1) \). This shows all rational zeros \( x = 1, \ x = \frac{3}{2}, \ -1 \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Polynomial Factorization
Polynomial factorization involves breaking down a complex polynomial into a product of simpler polynomials. This helps in understanding the polynomial's structure and finding its roots. When you perform polynomial factorization, you are expressing the original polynomial as a multiplication of its factors.
- Start by identifying the polynomial equation. In this case: \( P(x) = 2x^3 - 3x^2 - 2x + 3 \).
- Determine the polynomial's roots, as these will help you form the factors. The roots here are \( x=1 \), \( x=\frac{3}{2} \), and \( x=-1 \).
- Write these roots as factors: \( x-1 \), \( 2x-3 \), and \( x+1 \).
- Finally, multiply these factors to check that they expand back to the original polynomial.
Synthetic Division
Synthetic division is a simplified form of polynomial division, used to find roots or zeroes of polynomials quickly. It uses less complicated arithmetic and focuses on coefficients rather than variables. To use synthetic division:
- Take one possible zero, say \( x = 1 \), and use it in a synthetic division setup with your polynomial's coefficients: \( 2, -3, -2, 3 \).
- Place the possible zero on the left and set up the row of coefficients on the right.
- Bring down the first coefficient. Multiply it by the zero and add to the next coefficient. This is repeated across the row.
- If the result at the last coefficient position is zero, the tested value is indeed a root.
Rational Zeros
Rational zeros are the solutions to the polynomial equation that can be expressed as fractions. According to the Rational Root Theorem, if there's a rational zero \( \frac{p}{q} \), then \( p \) is a factor of the constant term and \( q \) is a factor of the leading coefficient.
- Identify potential rational zeros by calculating these factors. For \( P(x) = 2x^3 - 3x^2 - 2x + 3 \), the constant term is 3, and the leading coefficient is 2.
- Possible zeros are \( \pm 1, \pm 3, \pm \frac{1}{2}, \pm \frac{3}{2} \).
- Test these using synthetic division to see if they actually satisfy the polynomial equation (resulting in a remainder of zero).
- This can greatly simplify the process of finding all zeros of a polynomial without extensive guesswork.