We are able to find an equation of a line knowing its gradient and a point it passes through.

Let's say we want to find an equation of a line with a gradient 2, passing through the point (4, 5).

Start with a general equation of a straight line **y = mx + c**.

**m** represents the gradient, **c** represents the y-intercept.

We know the gradient, so we can replace m with 2.

This gives us y = 2x + c.

To work out the value of c, substitute the coordinates of the point given in the question.

The coordinates here are (4, 5), so x = 4 and y = 5.

5 = 2 × 4 + c

5 = 8 + c

5 - 8 = c

-3 = c

Now let's put everything together to get the equation **y = 2x - 3**.

It is also useful to know that **parallel lines** have the same gradient. You can use this property of straight lines when the question does not specifically tell you what the gradient is.