### Introduction

Probably the most important function and graph that you will use are those associated with the straight line. A large number of relationships between engineering variables can be described using a straight line or linear graph. Even when this is not strictly the case it is often possible to approximate a relationship by a straight line. In this Section we study the equation of a straight line, its properties and graph.

#### Prerequisites

• understand what is meant by a function
• be able to graph simple functions

#### Learning Outcomes

• recognise the equation of a straight line
• explain the significance of $a$ and $b$ in the equation of a line $f\left(x\right)=ax+b$
• find the gradient of a straight line given two points on the line
• find the equation of a straight line through two points
• find the distance between two points