Equation of a straight line

Equations and graphs Equation of a straight line

This equation $y = 2x + 1$ is one example of an equation of a straight line. There are many others. All equations of a straight line have two defining properties.

We can examine the first of these properties by looking at the table below. It shows that when $x = 0$ , $y = 1$

$x$	-1	0	1	2	3	4
$y$	-1	1	3	5	7	9

Let’s look at some other straight line equations to see what the value of $y$ is when $x = 0$

Equation	Value of $y$ when $x = 0$
$y = 5x + 2$	2
$y = 5x + 3$	3
$y = -7x + 2$	2
$y = -7x - 7$	-7
$y = 10x + 99$	99

We can see that the value of $y$ when $x = 0$ is the constant that has been added or subtracted in the equation of a straight line.

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