# Finding Rational Zeros

## Simplifying Polynomials: The Power of Factoring

Solving long and complicated polynomials can often feel like an intimidating task, and the fear of making careless errors can loom over the process. However, there is a helpful technique that can make dealing with these expressions much more manageable - factoring! In this article, we will delve into a method known as finding rational zeros, which can effectively and accurately factor polynomials.

## Understanding Rational Zeros

Firstly, it's essential to understand the terms zero and rational zero in relation to polynomials. A zero is any value of x that makes the polynomial equal to zero, also referred to as the root of the polynomial. A rational zero is a rational number, which is a fraction of two integers, that is also a root of the polynomial. It's worth noting that an irrational zero is a number that cannot be expressed as a fraction and is usually represented by a never-ending non-repeating decimal.

To fully grasp this concept, let's also revisit the definition of the standard form of a polynomial. A polynomial in standard form is written as f(x) = anxn + an-1xn-1 + ... + a1x + a0, where an, an-1, ..., a1, and a0 are the coefficients of the polynomial.

## The Rational Zeros Theorem

Now, let's explore the method of finding rational zeros - the Rational Zeros Theorem. This theorem states that if a polynomial has integer coefficients, then all rational zeros of that polynomial will have the form p/q, where p is a factor of the constant term (a0) and q is a factor of the leading coefficient (an).

Before identifying potential rational roots, it's crucial to factor out the greatest common divisor (GCF) of the polynomial. It's important to note that the Rational Zeros Theorem only applies to rational zeros, and not all the roots of a polynomial can be found using this method.

## Implementing the Rational Zeros Theorem

Let's put the Rational Zeros Theorem into practice with a few examples:

### Finding Possible Rational Zeros of a Polynomial

In this section, we will list all the potential rational roots of a given polynomial. It's worth noting that we won't be determining the correct set of rational zeros in this section, which will be done in the following section. The main objective here is to gain a deeper understanding of the Rational Zeros Theorem.

For instance, if we are given the polynomial f(x) = 2x3 - 5x2 + 4, the possible values for p are all the factors of 4 (the constant term), namely 1, 2, and 4. Similarly, the possible values for q are all the factors of 2 (the leading coefficient), which are 1 and 2.

By combining the values of p and q, we can determine that the potential rational zeros are 1/1, 1/2, 2/1, and 2/2, which can be simplified to 1, 1/2, 2, and 1. Eliminating any duplicates, we obtain the final list of possible rational zeros: 1 and 1/2.

### Finding Rational Zeros of a Polynomial

In this section, we will determine the set of rational zeros that satisfy a given polynomial. This method enables us to factor the polynomial and accurately solve the expression. The main steps to follow are as follows:

• List all the possible zeros using the Rational Zeros Theorem.
• Perform synthetic division to evaluate the polynomial at each value of rational zeros in the first step.
• Note down the quotient if the remainder is 0.
• Repeat steps 1-3 for the quotient obtained.

Let's look at an example to better understand this process. If we are given the polynomial f(x) = 6x2 - 19x + 14, we can factor out the GCF (1) and obtain x2 - 19x + 14. Using the Rational Zeros Theorem, the possible rational zeros are 1, 2, 7, and 14.

Upon performing synthetic division, we find that the remainder is 0 when we divide by 2. This indicates that 2 is a rational zero, and the quotient is x - 9. Repeating the process with x - 9, we determine that the other rational zero is 9. Hence, the set of rational zeros that satisfy f(x) = 6x2 - 19x + 14 is {2, 9}.

In short, finding rational zeros is a useful technique for factoring and solving polynomials. With the Rational Zeros Theorem, we can efficiently determine potential rational zeros and factor polynomials with ease. With practice, you'll become more comfortable with this method and can solve even the most complex polynomials accurately.

## Finding Rational Zeros using the Rational Zeros Theorem

When solving polynomial equations that are easily factored or of degree 2, it is crucial to understand how to find rational zeros. In this article, we will go through a step-by-step process for finding rational zeros using the Rational Zeros Theorem, supplemented by examples for better comprehension.

## Step 1: Listing Potential Rational Zeros

The initial step is to utilize the Rational Zeros Theorem to list all possible rational zeros in the form of p/q, where p is a factor of the constant term and q is a factor of the leading coefficient. This will give us a list of potential solutions.

## Step 2: Utilizing Synthetic Division

Next, we will use synthetic division to evaluate the polynomial at each of the rational zeros listed in Step 1. If we obtain a remainder of 0, then the corresponding value is a solution. This method allows us to eliminate any potential zeros that are not actual solutions.

## Step 3: Factoring and Repeating the Process

After finding the first solution, we will factor the polynomial using the found root. This will give us a quotient, which we will then repeat the process on, starting from Step 1. Repeating this process will help us to uncover any additional rational zeros and their multiplicities.

## Step 4: Evaluating the Remaining Solutions

The final step is to solve the remaining quadratic equation either by factoring or using the quadratic formula. This will give us the remaining solutions for the polynomial equation.

• Example 1:

Find all rational zeros of the polynomial f(x) = x^3 - 12x^2 + x + 12.

Step 1: The possible rational zeros are ±1, ±2, ±3, ±4, ±6, ±12.

Step 2: Using synthetic division, we find that -1 is a solution with a multiplicity of 1. The quotient is x^2 - 11x + 12.

Step 3: The possible rational zeros for the quotient are ±1, ±2, ±3, ±4, ±6, ±12.

Using synthetic division again, we find that -1 is a solution with a multiplicity of 2. The quotient is x - 3.

Step 4: The remaining solutions are x = 3, 4, and -1.

The fully factored expression for f(x) is (x + 1)(x - 3)(x - 4).

This shows that the rational zeros of f(x) are x = -1, 3, and 4.

• Example 2:

Find all rational zeros of the polynomial f(x) = x^3 - 14x^2 + 27x - 14.

Step 1: The possible rational zeros are ±1, ±2, ±7, ±14.

Step 2: Using synthetic division, we find that -1 is a solution with a multiplicity of 1. The quotient is x^2 - 13x + 14.

Step 3: The possible rational zeros for the quotient are ±1, ±2, ±7, ±14.

Using synthetic division, we find that 2 is a solution with a multiplicity of 1. The quotient is x - 7.

Step 4: The remaining solution is x = 7.

The fully factored expression for f(x) is (x + 1)(x - 2)(x - 7).

This shows that the rational zeros of f(x) are x = -1, 2, and 7.

## Applying the Rational Zeros Theorem in Geometry

The Rational Zeros Theorem can also be useful in a geometry context, as demonstrated in the following example.

Amy is trying to determine the dimensions of a box with a volume of 24 cm^3. She knows that the width is 2 cm more than the height, and the length is 3 cm less than the height. To solve this, we can utilize the Rational Zeros Theorem and the method utilized in the examples above.

## Recalling Descartes' Rule of Signs

Before beginning, let us first remind ourselves of Descartes' Rule of Signs.

Descartes' Rule of Signs:

If a polynomial has real coefficients, the number of positive real zeros is either equal to the number of sign changes in p(x) or is less than that by an even whole number. The number of negative real zeros is either equal to the number of sign changes in p(-x) or is less than that by an even whole number.

## Solving the Problem

Step 1: Let the unknown dimensions of the box be h, h+2, and h-3. A sketch of this is shown below.

Height = h cm

Width = (h+2) cm

Length = (h-3) cm