## Function Zeros - Introduction

Understanding the concept of function zeros is crucial in mathematics. When you study polynomial, exponential, or other types of functions, knowing how to find their zeros can help solve equations and understand the behaviour of graphs.

### What are Function Zeros?

**Function zeros** are the values of the variable for which the value of the function becomes zero. In simpler terms, if you have a function \(f(x)\), the zeros are the points where \(f(x) = 0\). To find these points, you solve the equation \(f(x) = 0\).For example, if you have a function \(f(x) = x^2 - 4\), you set \(x^2 - 4 = 0\) and solve for \(x\).

A **function zero** (or root) is the value of \(x\) that satisfies the equation \(f(x) = 0\).

### Finding Function Zeros

To find the zeros of a function, follow these general steps:

- Set the function equal to zero: \(f(x) = 0\)
- Solve the resulting equation for \(x\)

**Example:**Consider the quadratic function \(f(x) = x^2 - 4\). To find the zeros, you set the function to zero:\(x^2 - 4 = 0\)We can factor this equation as:\((x - 2)(x + 2) = 0\)Setting each factor to zero gives:\(x - 2 = 0\) or \(x + 2 = 0\)So, the zeros are \(x = 2\) and \(x = -2\).

### Importance of Function Zeros in Graphs

Zeros of a function are also known as **x-intercepts**. These are the points where the graph of the function crosses the x-axis. Knowing the zeros helps you plot the graph accurately.

The number of zeros a polynomial function has is equal to its degree. For example, a quadratic function can have up to two zeros.

### Special Cases and Multiple Zeros

Sometimes, functions can have multiple zeros or **repeated zeros**. When a zero is repeated, it means the factor corresponding to that zero appears more than once in the factored form of the function. For instance, in the function \(f(x) = (x - 1)^2\), the zero \(x = 1\) is repeated.Let's consider an example to understand this better.

**Example:**Consider the function \(f(x) = (x - 3)^3\). To find the zeros:\((x - 3)^3 = 0\)We solve for \(x\):\(x - 3 = 0\)Thus, the zero is \(x = 3\). Since the factor \((x - 3)\) appears three times, \(x = 3\) is a repeated zero with a multiplicity of three.

Sometimes, finding zeros can be complicated, especially for higher degree polynomials. Advanced methods like synthetic division, use of graphing calculators, or numerical techniques such as Newton-Raphson method might be necessary. Newton-Raphson method is an iterative technique which starts with an initial guess and improves it repeatedly using the formula:\[ x_{n+1} = x_n - \frac{f(x_n)}{f'(x_n)} \]Here, \(x_n\) is the current guess, \(f(x_n)\) is the function value at \(x_n\), and \(f'(x_n)\) is the derivative value at \(x_n\). This method is particularly useful when you need a precise approximation of zeros.

## How to Find the Zeros of a Polynomial Function

Finding the zeros of a polynomial function is an essential part of understanding the function's behaviour. It allows you to know where the function intersects the x-axis and helps in solving equations.

### Methods to Find Zeros of Polynomial Functions

There are several methods to find the zeros of polynomial functions. These methods include factoring, using the quadratic formula, and graphing. Each of these methods can be used depending on the complexity of the polynomial.

**Example:**For the quadratic function \( f(x) = x^2 - 5x + 6 \), you can use factoring to find the zeros:Set \( f(x) = 0 \):\[ x^2 - 5x + 6 = 0 \]Factor the quadratic equation:\[ (x - 2)(x - 3) = 0 \]Solve for \( x \):\[ x - 2 = 0 \] or \[ x - 3 = 0 \]So the zeros are \( x = 2 \) and \( x = 3 \).

### Using the Quadratic Formula

For quadratic functions that cannot easily be factored, you can use the quadratic formula. The quadratic formula is:\[ x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} \]Where \( a \), \( b \), and \( c \) are coefficients from the quadratic equation \( ax^2 + bx + c = 0 \).

When using the quadratic formula, ensure the discriminant \( b^2 - 4ac \) is greater than or equal to zero. If it is less than zero, the quadratic equation has no real zeros.

**Example:**Consider the quadratic function \( f(x) = 2x^2 - 4x + 1 \).Set \( f(x) = 0 \):\[ 2x^2 - 4x + 1 = 0 \]Using the quadratic formula,\[ x = \frac{-(-4) \pm \sqrt{(-4)^2 - 4 \cdot 2 \cdot 1}}{2 \cdot 2} \]This simplifies to:\[ x = \frac{4 \pm \sqrt{16 - 8}}{4} \]\[ x = \frac{4 \pm \sqrt{8}}{4} \]\[ x = \frac{4 \pm 2\sqrt{2}}{4} \]\[ x = 1 \pm \frac{\sqrt{2}}{2} \]Therefore, the zeros are:\[ x = 1 + \frac{\sqrt{2}}{2} \] and \[ x = 1 - \frac{\sqrt{2}}{2} \].

### Graphing to Find Zeros

Graphing is another effective method for finding the zeros of polynomial functions. When you graph a function, the points where the graph intersects the x-axis are the function's zeros. This method can be particularly useful for higher-degree polynomials or those that do not factor easily.

For more complex polynomials, tools such as graphing calculators or software can be used to approximate the zeros. These tools plot the graph and give a visual indication of where the zeros are. Some advanced software can also provide numerical solutions to a high degree of accuracy.

### Special Cases Involving Zeros

In some cases, polynomial functions may have **repeated zeros**. These are zeros that occur more than once. For example, if a polynomial function has a zero at \( x = 2 \) and it is repeated three times, it is said to have a multiplicity of three at that zero.

**Example:**Consider the function \( f(x) = (x - 2)^3 \). To find the zeros, you set \( f(x) = 0 \):\[ (x - 2)^3 = 0 \]Solve for \( x \):\[ x - 2 = 0 \]So the zero is \( x = 2 \). Since \( (x - 2) \) is repeated three times, \( x = 2 \) has a multiplicity of three.

## Techniques to Find Function Zeros

Understanding various techniques to find function zeros is important for solving mathematical equations and analysing functions. Here are some common methods you can use.

### Factoring

Factoring is a straightforward method to find the zeros of polynomial functions. To use this technique, you express the polynomial in its factored form and set each factor equal to zero.

**Example:**Consider the function \(f(x) = x^2 - 5x + 6\). To find the zeros, you factorise it as:\[x^2 - 5x + 6 = (x - 2)(x - 3)\]Then, set each factor to zero:\[x - 2 = 0\] or \[x - 3 = 0\]So, the zeros are \(x = 2\) and \(x = 3\).

### Using the Quadratic Formula

When factoring is not feasible, you can use the quadratic formula. This is especially handy for solving quadratic equations (polynomials of degree 2).

The **quadratic formula** is given by:\[x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}\]Here, \(a\), \(b\), and \(c\) are coefficients from the equation \(ax^2 + bx + c = 0\).

Ensure that the discriminant \(b^2 - 4ac\) is non-negative. If it's negative, the quadratic equation has no real zeros.

**Example:**For the function \(f(x) = 2x^2 - 4x + 1\), set \(f(x) = 0\) and use the quadratic formula:\[2x^2 - 4x + 1 = 0\]Applying the quadratic formula:\[x = \frac{-(-4) \pm \sqrt{(-4)^2 - 4 \cdot 2 \cdot 1}}{2 \cdot 2}\]\[x = \frac{4 \pm \sqrt{16 - 8}}{4}\]\[x = \frac{4 \pm \sqrt{8}}{4}\]\[x = \frac{4 \pm 2\sqrt{2}}{4}\]\[x = 1 \pm \frac{\sqrt{2}}{2}\]The zeros are: \(x = 1 + \frac{\sqrt{2}}{2}\) and \(x = 1 - \frac{\sqrt{2}}{2}\).

### Graphing

Graphing is a useful method for visualising where a function intersects the x-axis. You can find the zeros by looking at the x-intercepts of the graph.

For higher-degree polynomials, graphing calculators or software can be advantageous. They help approximate zeros and provide a visual representation. Advanced tools can further employ numerical techniques like the Newton-Raphson method for higher precision. The Newton-Raphson formula is:\[ x_{n+1} = x_n - \frac{f(x_n)}{f'(x_n)} \]This iterative method starts with an initial guess and refines it to find an accurate approximation of the zero.

### Special Cases and Repeated Zeros

In some functions, zeros might be repeated, known as **multiple or repeated zeros**. A zero is repeated if its corresponding factor appears more than once in the polynomial's factored form.

**Example:**Consider the function \(f(x) = (x - 2)^3\). To find the zeros, set \(f(x) = 0\):\[(x - 2)^3 = 0\]Solving for \(x\):\[x - 2 = 0\]Thus, the zero is \(x = 2\). Since \(x - 2\) is repeated three times, \(x = 2\) is a zero with a multiplicity of three.

The multiplicity of a zero affects the shape of the graph at that point. A zero with an even multiplicity will touch the x-axis and turn around, while a zero with an odd multiplicity will cross the x-axis.

## How to Find the Zeros of a Quadratic Function

Finding the zeros of a quadratic function is an essential step in solving equations and understanding the behaviour of the function. Quadratic functions have the general form \( ax^2 + bx + c \) and can have up to two zeros.

### Zeros of a Function Explained

**Function zeros**, also known as roots, are the values of the variable for which the function equals zero. In mathematical terms, if a function \( f(x) \) has a zero at \( x = a \), then \( f(a) = 0 \). For quadratic functions, finding the zeros involves solving the equation \( ax^2 + bx + c = 0 \).

### Steps for Finding Zeros of a Polynomial Function

To find the zeros of a polynomial function, follow these steps:

- Step 1: Set the function equal to zero. For a quadratic function, this means \( ax^2 + bx + c = 0 \).
- Step 2: Solve the resulting equation for \( x \). This can be done using different methods like factoring, the quadratic formula, or completing the square.

**Example:**Consider the quadratic function \( f(x) = x^2 - 5x + 6 \).Step 1: Set it equal to zero:\[ x^2 - 5x + 6 = 0 \]Step 2: Solve the equation. In this case, factoring works:\[ (x - 2)(x - 3) = 0 \]Set each factor to zero:\[ x - 2 = 0 \] and \[ x - 3 = 0 \]So, the zeros are \( x = 2 \) and \( x = 3 \).

### Graphical Method to Find Function Zeros

Using graphs is a visual method to find function zeros. When you plot a quadratic function, the points at which the graph intersects the x-axis are the zeros.

If the graph touches the x-axis at one point and turns back, that point is a repeated zero or has a multiplicity greater than one.

Function | Zeros |

\(f(x) = x^2 - 4x + 4\) | \(x = 2\) (repeated zero) |

\(f(x) = x^2 - 5x + 6\) | \(x = 2\), \(x = 3\) |

### Using Factoring to Find the Zeros of a Quadratic Function

Factoring is one of the most straightforward methods to find the zeros of a quadratic function. You express the quadratic equation in its factored form and set each factor to zero.

**Example:**Consider the quadratic function \( f(x) = x^2 - 6x + 9 \).Factor the quadratic equation:\[ x^2 - 6x + 9 = (x - 3)^2 \]Set the factored form to zero:\[ (x - 3)^2 = 0 \]Solve for \( x \):\[ x - 3 = 0 \]Thus, the zero is \( x = 3 \). This is a repeated zero with a multiplicity of two.

### Finding Zeros of a Polynomial Function Using Synthetic Division

Synthetic division is an algorithmic approach used to find zeros of polynomial functions. This method simplifies the process, especially for higher-degree polynomials.

To find the zeros using synthetic division, you need to perform the following steps:

- Step 1: Choose a potential zero of the polynomial. You can use the Rational Root Theorem to identify possible candidates.
- Step 2: Use synthetic division to divide the polynomial by \(x - c \), where \(c \) is a potential zero.
- Step 3: Check the remainder. If the remainder is zero, then \(c \) is a zero of the polynomial.

x | | 2 -3 -8 3 |

1 | | 2 -1 -9 -6 |

2 -1 -9 0 |

### Solving Quadratic Equations to Find Function Zeros

To find the zeros of a quadratic equation, you can also use the quadratic formula, which works for all quadratic equations.

**Example:**Given the quadratic function \( f(x) = 2x^2 - 4x + 1 \), use the quadratic formula:\[x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}\]Substitute the coefficients \( a = 2 \), \( b = -4 \), and \( c = 1 \):\[x = \frac{-(-4) \pm \sqrt{(-4)^2 - 4(2)(1)}}{2(2)}\]This simplifies to:\[x = \frac{4 \pm \sqrt{16 - 8}}{4}\]\[x = \frac{4 \pm \sqrt{8}}{4}\]\[x = \frac{4 \pm 2\sqrt{2}}{4}\]\[x = 1 \pm \frac{\sqrt{2}}{2}\]Thus, the zeros are \( x = 1 + \frac{\sqrt{2}}{2} \) and \( x = 1 - \frac{\sqrt{2}}{2} \).

## Function zeros - Key takeaways

**Function Zeros:**Values of the variable at which the function's value is zero, also known as roots. For instance, in the function f(x) = x^{2}- 4, you solve x^{2}- 4 = 0 to find the zeros.**Finding Function Zeros:**Involves setting the function equal to zero and solving the equation f(x) = 0. This can be done through various methods, such as factoring, using the quadratic formula, or graphing.**Importance of Zeros in Graphs:**Function zeros are the points where the graph intersects the x-axis, also called x-intercepts.**Repeated Zeros:**These occur when a zero appears multiple times in the factored form of the function. For example, in f(x) = (x - 1)^{2}, the zero x = 1 is repeated.**Techniques to Find Zeros:**Different methods like factoring, quadratic formula, synthetic division, and iterative numerical techniques (e.g., Newton-Raphson method) can be used to determine the zeros of polynomial functions.

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