Math Problem Statement

solve

The function below has at least one rational zero. Use this fact to find all zeros of the function. h(x) = 6x^3 + 31x^2 + 4x - 5

Solution

To solve this problem, we can use the Rational Zeros Theorem, which states that if a polynomial has rational zeros, then they are in the form ±pq\pm \frac{p}{q}, where:

  • pp is a factor of the constant term.
  • qq is a factor of the leading coefficient.

The polynomial given is:

h(x)=6x3+31x2+4x5h(x) = 6x^3 + 31x^2 + 4x - 5

Step 1: Identify Possible Rational Zeros

  • The constant term is 5-5, so its factors (pp) are ±1,±5\pm 1, \pm 5.
  • The leading coefficient is 66, so its factors (qq) are ±1,±2,±3,±6\pm 1, \pm 2, \pm 3, \pm 6.

Using the Rational Zeros Theorem, the possible rational zeros are:

±1,±12,±13,±16,±5,±52,±53,±56\pm 1, \pm \frac{1}{2}, \pm \frac{1}{3}, \pm \frac{1}{6}, \pm 5, \pm \frac{5}{2}, \pm \frac{5}{3}, \pm \frac{5}{6}

Step 2: Test Possible Zeros Using Synthetic Division

We will test these potential zeros by plugging them into the polynomial to find which one(s) result in h(x)=0h(x) = 0. A common approach is to start with the simplest candidates, such as ±1\pm 1.

  1. Test x=1x = 1: h(1)=6(1)3+31(1)2+4(1)5=6+31+45=36(0)h(1) = 6(1)^3 + 31(1)^2 + 4(1) - 5 = 6 + 31 + 4 - 5 = 36 \quad (\neq 0)

  2. Test x=1x = -1: h(1)=6(1)3+31(1)2+4(1)5=6+3145=16(0)h(-1) = 6(-1)^3 + 31(-1)^2 + 4(-1) - 5 = -6 + 31 - 4 - 5 = 16 \quad (\neq 0)

  3. Test x=5x = 5: h(5)=6(5)3+31(5)2+4(5)5=6(125)+31(25)+205=750+775+205=1540(0)h(5) = 6(5)^3 + 31(5)^2 + 4(5) - 5 = 6(125) + 31(25) + 20 - 5 = 750 + 775 + 20 - 5 = 1540 \quad (\neq 0)

  4. Test x=5x = -5: h(5)=6(5)3+31(5)2+4(5)5=6(125)+31(25)205=750+775205=0h(-5) = 6(-5)^3 + 31(-5)^2 + 4(-5) - 5 = 6(-125) + 31(25) - 20 - 5 = -750 + 775 - 20 - 5 = 0

Since h(5)=0h(-5) = 0, x=5x = -5 is a zero.

Step 3: Perform Polynomial Division

Now that x=5x = -5 is a zero, we divide h(x)h(x) by x+5x + 5. We can use synthetic division for this:

  • Perform synthetic division:
-5
6314
-30
----------------------
61-1

The quotient is 6x2+x16x^2 + x - 1.

Step 4: Factor the Quotient

We now have:

h(x)=(x+5)(6x2+x1)h(x) = (x + 5)(6x^2 + x - 1)

To find the remaining zeros, we solve 6x2+x1=06x^2 + x - 1 = 0. We can factor this quadratic equation by finding two numbers that multiply to 6-6 and add to 11. Factoring yields:

6x2+x1=(3x1)(2x+1)6x^2 + x - 1 = (3x - 1)(2x + 1)

Step 5: Find All Zeros

Setting each factor equal to zero:

  1. x+5=0x + 5 = 0 gives x=5x = -5.
  2. 3x1=03x - 1 = 0 gives x=13x = \frac{1}{3}.
  3. 2x+1=02x + 1 = 0 gives x=12x = -\frac{1}{2}.

Final Answer

The zeros of h(x)h(x) are:

x=5,x=13,x=12x = -5, \quad x = \frac{1}{3}, \quad x = -\frac{1}{2}

Would you like more details, or have any questions on this? Here are five related questions for further understanding:

  1. What is the Rational Zeros Theorem, and how does it help in finding zeros of a polynomial?
  2. Can all polynomials have rational zeros? Why or why not?
  3. How is synthetic division performed, and why is it used in this context?
  4. What should be done if a polynomial has no rational zeros but still needs all zeros found?
  5. What are the steps to factor a quadratic expression, and when is it necessary?

Tip: When using the Rational Zeros Theorem, always start with simpler factors like ±1\pm 1 to quickly find rational zeros before testing more complex possibilities.

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Math Problem Analysis

Mathematical Concepts

Algebra
Polynomials
Rational Zeros Theorem
Synthetic Division

Formulas

Rational zeros in the form ±p/q, where p is a factor of the constant term, and q is a factor of the leading coefficient

Theorems

Rational Zeros Theorem

Suitable Grade Level

Grades 10-12