## Function Modelling Definition

Function modelling is a fundamental concept in mathematics used to describe the relationship between variables. Whether you're working on algebra, geometry, or calculus, understanding how to create and use models can help you comprehend complex mathematical relationships. In this section, you will learn about function modelling, with clear explanations and examples.

### What is Function Modelling?

**Function modelling** involves representing real-world situations with mathematical functions. These models help simplify and solve problems by expressing relationships in a mathematical form.

The main goal of function modelling is to develop equations or functions that closely match real-world phenomena. You can use various types of functions, including linear, quadratic, polynomial, exponential, and logarithmic functions, depending on the nature of the problem you're analysing.

For example, if you’re studying the growth of a plant over time, an exponential function might be a suitable model. Function modelling allows us to:

- Predict future values
- Understand relationships between variables
- Find optimised solutions to problems

### Basic Components of a Function Model

To create a function model, you need to identify the components that define the relationship between the variables:

**Independent Variable**: The variable that you can control or choose. It is usually denoted as*x*.**Dependent Variable**: The variable that depends on the independent variable. It is often denoted as*y*.**Function Rule**: The mathematical equation that defines the relationship between the independent and dependent variables.

Consider a simple linear function model that represents the relationship between the number of hours you study (independent variable) and your test score (dependent variable).

If the relationship is linear, the function rule might look something like this:

Equation:

\[ y = 5x + 50 \]

Here: \( y \) = Test score, \( x \) = Hours of study, 5 = The rate of increase in the test score per hour of study, 50 = The base score.

### Types of Functions in Modelling

Various functions can be used in modelling depending on the nature of the problem:

**Linear Functions**: Represented by*y = mx + b*, where*m*is the slope and*b*is the y-intercept.**Quadratic Functions**: Represented by*y = ax^2 + bx + c*, commonly used in physics and engineering.**Polynomial Functions**: Involving terms like*ax^n*, and used for more complex relationships.**Exponential Functions**: Represented by*y = a \cdot b^x*, suitable for growth and decay problems.**Logarithmic Functions**: Represented by*y = a \log(x) + b*, used in contexts like sound intensity and earthquake measurements.

Always check the data carefully before determining which function best fits a real-world problem.

Let's delve deeper into quadratic functions. Quadratic functions are represented as:

\( y = ax^2 + bx + c \)

These models are widely used to describe projectile motion, where objects are thrown or propelled. For example, if you throw a ball, the path it takes can be modelled by a quadratic function.

In a quadratic function, the term \( ax^2 \) causes the parabola to open up or down depending on the sign of *a*. If:

*a*is positive, the parabola opens upward.*a*is negative, the parabola opens downward.

A typical example is the height *h* of a ball at time *t* seconds given by:

\( h(t) = -16t^2 + v_0 t + h_0 \)

where:

- -16 is the acceleration due to gravity (in feet/second^2),
- \( v_0 \) is the initial velocity, and
- \( h_0 \) is the initial height.

## Functions as Models

Function modelling is a powerful tool in mathematics that helps you understand and predict relationships between variables. This section will provide insights into the usage of functions as models by discussing their definition, components, and different types.

### What is Function Modelling?

**Function modelling** involves representing real-world situations with mathematical functions. These models help simplify and solve problems by expressing relationships in a mathematical form.

Function modelling aims to develop equations or functions that closely represent real-world phenomena. Depending on the complexity of the problem, various types of functions can be used, such as linear, quadratic, polynomial, exponential, and logarithmic functions.

If you are analysing the growth of a plant over time, an exponential function might be the appropriate model. Function modelling allows you to:

- Predict future values
- Understand relationships between variables
- Find optimised solutions to problems

### Basic Components of a Function Model

Creating a function model requires you to identify the key components that define the relationship between variables:

**Independent Variable**: This is the variable you control or choose, usually denoted as*x*.**Dependent Variable**: This variable depends on the independent variable, often denoted as*y*.**Function Rule**: The mathematical equation that defines the relationship between the independent and dependent variables.

Consider a simple linear function model that represents the relationship between the number of hours you study (independent variable) and your test score (dependent variable).

If the relationship is linear, the function rule might look something like this:

Equation:

\[ y = 5x + 50 \]

Here: \( y \) = Test score, \( x \) = Hours of study, 5 = The rate of increase in the test score per hour of study, 50 = The base score.

### Types of Functions in Modelling

Different types of functions can serve as models depending on the problem:

**Linear Functions**: Represented by*y = mx + b*, with*m*as the slope and*b*as the y-intercept.**Quadratic Functions**: Represented by*y = ax^2 + bx + c*. Common in physics and engineering applications.**Polynomial Functions**: Include terms like*ax^n*. Used for more complex relationships.**Exponential Functions**: Represented by*y = a \cdot b^x*. Suitable for growth and decay problems.**Logarithmic Functions**: Represented by*y = a \log(x) + b*. Applies in contexts like sound intensity and earthquake measurements.

Always check your data carefully before choosing the function that best fits a real-world problem.

Let's delve deeper into quadratic functions. Quadratic functions are represented as:

\( y = ax^2 + bx + c \)

These models are widely used to describe projectile motion, where objects are thrown or propelled. For example, if you throw a ball, the path it takes can be modelled by a quadratic function.

In a quadratic function, the term \( ax^2 \) causes the parabola to open up or down depending on the sign of *a*. If:

*a*is positive, the parabola opens upward.*a*is negative, the parabola opens downward.

When applying quadratic functions in real-world scenarios, you often need to determine the maximum height or the time at which the maximum height is reached.

A typical example is the height *h* of a ball at time *t* seconds given by:

\( h(t) = -16t^2 + v_0 t + h_0 \)

where:

- -16 is the acceleration due to gravity (in feet/second^2),
- \( v_0 \) is the initial velocity, and
- \( h_0 \) is the initial height.

## Modelling with Linear Functions

Modelling with linear functions is an effective technique used to represent and solve real-world problems. Linear functions are characterised by a constant rate of change, making them suitable for situations where changes are consistent over time.

### Examples of Function Modelling with Linear Functions

A simple example of function modelling using linear functions is determining the relationship between distance travelled and time. Suppose you travel at a constant speed:

Equation:

\[ d = rt \]

Here:\(d\) = Distance travelled,\(r\) = Speed,\(t\) = Time.

If you travel at a speed of 60 km/h, the linear function becomes:

\[ d = 60t \]

This model shows that for every hour you travel, you cover 60 kilometres. The graph of this function is a straight line with a slope of 60, passing through the origin (0,0).

Linear function models are particularly useful for financial calculations, such as predicting costs or profits over time.

Let's explore how linear functions can be applied to calculate expenses in a business setting. Consider a company that produces gadgets and incurs both fixed and variable costs:

Equation:

\[C = F + Vx\]

Here:\(C\) = Total cost,\(F\) = Fixed cost,\(V\) = Variable cost per unit,\(x\) = Number of units produced.

Assume the fixed costs (\(F\)) are $500, and the variable cost per unit (\(V\)) is $10. The linear function representing the total cost is:

\[C = 500 + 10x\]

This model allows the company to predict the total cost (\(C\)) for any number of units produced (\(x\)). By analysing these numbers, better budgeting and cost management decisions can be made.

## Modelling with Quadratic Functions

Quadratic functions are a cornerstone of mathematical modelling, allowing you to understand relationships and make predictions about data that follows a curved trajectory. These functions are particularly useful in physics, economics, and various engineering fields. In this section, you will explore how to model real-world problems using quadratic functions.

### Examples of Function Modelling with Quadratic Functions

One practical example of using quadratic functions is to model the trajectory of a projectile. If you throw a ball, its path can be described by the formula:

\( y = ax^2 + bx + c \)

Here:\( y \) = Height of the ball,\( x \) = Horizontal distance,\( a, b, c \) = Constants that depend on initial conditions.

If the initial velocity of the ball is *v _{0}* and the angle of projection is

*θ*, the height

*y*at any horizontal distance

*x*can be represented as:

\[ y = -\frac{g}{2v_0^2\text{cos}^2(θ)} x^2 + \text{tan}(θ) x + h_0 \]

where:

- \( g \) = Acceleration due to gravity (9.8 m/s²),
- \( h_0 \) = Initial height.

Understanding the components of the quadratic equation helps in interpreting the real-world scenario effectively.

Let's further analyse quadratic functions in the context of profit maximisation. A business might use a quadratic function to model its revenue and cost functions to find the optimum production level:

Revenue function: \( R(x) = px - qx^2 \)

Cost function: \( C(x) = c_0 + cx \)

Here:\( R(x) \) = Revenue,\( x \) = Quantity sold,\( p \) = Price per unit,\( q \) = Coefficient representing the rate of price decrease.

\( C(x) \) = Cost,\( c_0 \) = Fixed cost,\( c \) = Variable cost per unit.

To maximise profit, you subtract the cost from the revenue:

Profit function: \( P(x) = R(x) - C(x) \)

This results in:

\[ P(x) = px - qx^2 - c_0 - cx \]

By finding the derivative and setting it to zero, you can determine the quantity *x* that maximises profit:

\[ \frac{dP}{dx} = p - 2qx - c = 0 \]

Solving for \( x \):

\[ x = \frac{p - c}{2q} \]

Using this value, businesses can adjust their production to ensure maximum profitability.

## Modelling Exponential Functions

Exponential functions are essential in understanding phenomena where growth or decay happens at a rate proportional to the current value. From population growth to radioactive decay, these functions can be effectively used for modelling a wide array of real-world situations.

### Examples of Function Modelling with Exponential Functions

**Exponential function** is typically represented as \( y = a \cdot b^x \), where:

- \( a \) is the initial value,
- \( b \) is the base of the exponential, and
- \( x \) is the exponent.

Suppose you want to model the growth of a bacterial population that doubles every hour. If you start with 100 bacteria, the model can be written as:

- Initial value \( a \) = 100
- Growth rate \( b \) = 2 (since the population doubles)

Therefore, the function becomes:

\[ y = 100 \cdot 2^x \]

After 5 hours, the population size can be calculated by substituting \( x \) with 5:

\[ y = 100 \cdot 2^5 \]

Thus, the population will be:

\[ y = 3,200 \text{ bacteria} \]

Exponential functions are often used in finance to calculate compound interest, making them valuable in economic planning.

Consider the concept of radioactive decay, where the quantity of a radioactive substance decreases over time. The decay of a substance can be modelled using an exponential function:

\[ A(t) = A_0 \cdot e^{-kt} \]

Here:

- \( A(t) \) = Amount of substance at time \( t \)
- \( A_0 \) = Initial amount of substance
- \( e \) = Euler's number (approximately 2.718)
- \( k \) = Decay constant
- \( t \) = Time

For instance, if you have an initial amount of 50 grams of a radioactive substance with a decay constant \( k \) of 0.03, the function can be written as:

\[ A(t) = 50 \cdot e^{-0.03t} \]

To find the amount remaining after 10 years, substitute \( t \) with 10:

\[ A(10) = 50 \cdot e^{-0.03 \cdot 10} \]

Calculating the above expression:

\[ A(10) = 50 \cdot e^{-0.3} \approx 50 \cdot 0.7408 \approx 37.04 \text{ grams} \]

Thus, after 10 years, approximately 37.04 grams of the substance will remain.

## Function modeling - Key takeaways

**Function Modelling Definition:**Function modelling involves representing real-world situations with mathematical functions to simplify and solve problems by expressing relationships in a mathematical form.**Components of Function Modelling:**Independent Variable (x), Dependent Variable (y), and the Function Rule, which is the mathematical equation defining their relationship.**Types of Functions:**Linear (y = mx + b), Quadratic (y = ax^2 + bx + c), Polynomial (ax^n), Exponential (y = a \b^x), and Logarithmic (y = a log(x) + b).**Examples of Function Modelling:**Using linear functions to model distance over time (d = rt), quadratic functions for projectile motion (y = ax^2 + bx + c), and exponential functions for bacterial population growth (y = 100 \times 2^x).**Applications:**Function modelling is used to predict future values, understand relationships between variables, and find optimised solutions to problems across various fields such as finance, engineering, and physics.

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