Math Problem Statement

Let P(x) = 2x^3 + x^2 - 13x + 6. (i) Find all rational zeros of the polynomial equation P(x) = 0. (ii) Write the polynomial P(x) in factored form (Hint: Using synthetic division).

Solution

Let us solve the given problem step by step.

The problem:

  1. P(x)=2x3+x213x+6P(x) = 2x^3 + x^2 - 13x + 6
    • (i) Find all rational zeros of P(x)=0P(x) = 0.
    • (ii) Write P(x)P(x) in factored form (hint: using synthetic division).

Step 1: Rational Root Theorem

To find rational zeros, the Rational Root Theorem suggests that any rational zero is of the form: ±pq\pm \frac{p}{q} where:

  • pp: factors of the constant term (6),
  • qq: factors of the leading coefficient (2).

Factors of 6: ±1,±2,±3,±6\pm 1, \pm 2, \pm 3, \pm 6
Factors of 2: ±1,±2\pm 1, \pm 2

Possible rational zeros are: ±1,±12,±2,±3,±32,±6\pm 1, \pm \frac{1}{2}, \pm 2, \pm 3, \pm \frac{3}{2}, \pm 6


Step 2: Test Possible Rational Roots

We test these values in P(x)=2x3+x213x+6P(x) = 2x^3 + x^2 - 13x + 6.

Testing x=1x = 1:

P(1)=2(1)3+(1)213(1)+6=2+113+6=4(Not a root).P(1) = 2(1)^3 + (1)^2 - 13(1) + 6 = 2 + 1 - 13 + 6 = -4 \quad \text{(Not a root)}.

Testing x=1x = -1:

P(1)=2(1)3+(1)213(1)+6=2+1+13+6=18(Not a root).P(-1) = 2(-1)^3 + (-1)^2 - 13(-1) + 6 = -2 + 1 + 13 + 6 = 18 \quad \text{(Not a root)}.

Testing x=2x = 2:

P(2)=2(2)3+(2)213(2)+6=16+426+6=0(Root found!).P(2) = 2(2)^3 + (2)^2 - 13(2) + 6 = 16 + 4 - 26 + 6 = 0 \quad \text{(Root found!)}.

So, x=2x = 2 is a root.


Step 3: Synthetic Division

Divide P(x)P(x) by x2x - 2 using synthetic division.

Synthetic Division Setup:

2 & 2 & 1 & -13 & 6 \\ & & 4 & 10 & -6 \\ \hline & 2 & 5 & -3 & 0 \\ \end{array}$$ The quotient is $$2x^2 + 5x - 3$$, and the remainder is 0. --- ### Step 4: Factorize $$2x^2 + 5x - 3$$ Now factorize $$2x^2 + 5x - 3$$. #### Using trial and error or grouping: $$2x^2 + 5x - 3 = (2x - 1)(x + 3)$$ --- ### Final Answer: 1. The rational zeros are: $$x = 2, x = \frac{1}{2}, x = -3$$. 2. The factored form of $$P(x)$$ is: $$P(x) = 2(x - 2)(x + 3)(2x - 1)$$ Would you like detailed steps for synthetic division or the factoring process? --- ### Related Questions: 1. What is the general method to apply the Rational Root Theorem? 2. How can synthetic division confirm if a root is valid? 3. What techniques can be used to factor a quadratic polynomial? 4. Why are only rational roots tested when using the Rational Root Theorem? 5. How can you verify the factors by multiplying them back? **Tip:** When using the Rational Root Theorem, always simplify $$\frac{p}{q}$$ to its lowest terms to avoid redundant testing.

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Math Problem Analysis

Mathematical Concepts

Polynomials
Rational Root Theorem
Synthetic Division
Factoring

Formulas

Rational Root Theorem: Possible roots are ±p/q, where p = factors of the constant term and q = factors of the leading coefficient.
Factoring: P(x) = (x - r1)(x - r2)... for roots r1, r2,...

Theorems

Rational Root Theorem

Suitable Grade Level

Grades 10-12