IGCSEMathsEdexcelMaths BRevision NotesFunctionsCoordinate GeometryLength of a Line

Length of a Line (Edexcel IGCSE Maths B): Revision Note

Exam code: 4MB1

Written by: Jamie Wood

Reviewed by: Dan Finlay

Updated on 20 January 2026

Length of a line

How do I calculate the length of a line?

The distance between two points with coordinates $(x_{1}, y_{1})$ and $(x_{2}, y_{2})$ can be found using the formula

$d = \sqrt{{(x_{1} - x_{2})}^{2} + {(y_{1} - y_{2})}^{2}}$

This formula uses Pythagoras’ theorem $a^{2} + b^{2} = c^{2}$
- It is applied to the difference in the $x$ -coordinates and the difference in the $y$ -coordinates

A right-angled triangle drawn between two point on a straight line, to show how Pythagoras is used to find the length of a line

Examiner Tips and Tricks

Be extra careful when negative coordinates are involved. It can help to put negative numbers in brackets to make your working clearer, e.g. $(- 6) - (- 8) = 2$ .

Worked Example

Point A has coordinates (3, -4) and point B has coordinates (-5, 2).

Calculate the distance of the line segment AB.

Answer:

Using the formula for the distance between two points, $d = \sqrt{{(x_{1} - x_{2})}^{2} + {(y_{1} - y_{2})}^{2}}$

Substitute in the two given coordinates

$d = \sqrt{{(3 - (- 5))}^{2} + {((- 4) - 2)}^{2}}$

Be careful with the negative numbers
$3 - (- 5) = 8$ and $(- 4) - 2 = - 6$

Simplify

$d = \sqrt{{(8)}^{2} + {(- 6)}^{2}} = \sqrt{64 + 36} = \sqrt{100} = 10$

10 units

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