The Straight Line: Use Pythagoras' Theorem to Calculate Distance between 2 Points
The Straight Line: Use Pythagoras’ Theorem to Calculate Distance between 2 Points
The Straight Line: Use Pythagoras’ Theorem to Calculate Distance Between Two Points
Understanding the Concept

Pythagoras’ Theorem states that in a rightangled triangle, the square of the hypotenuse (the side opposite the right angle) is equal to the sum of the squares of the other two sides. This can be represented as
a² = b² + c²
. 
When dealing with coordinates, treat each point as one corner of a rightangled triangle, and the distance between them as the hypotenuse.

The distance d between two points (x₁, y₁) and (x₂, y₂) can therefore be calculated with this formula remembering it comes directly from the theorem itself:
d = √[(x₂  x₁)² + (y₂  y₁)²]
.
Applying the Formula

First, determine the coordinates of the two points you are calculating distance between.

Subtract the xcoordinates and subtract the ycoordinates of these two points. This gives you the lengths of the other two sides of your rightangled triangle.

Square these lengths (raise to the power of 2).

Add the squares together.

The square root of this sum gives you the length of the hypotenuse, which is the distance between your two points.
Example Problems

To apply this to a problem, consider the points A(2,3) and B(6,7). The distance between A and B is:
d = √[(6  2)² + (7  3)²] = √[16 + 16] = √32
. 
Remember, the numbers representing the coordinates can be negative, in which case you may need to subtract a negative (which effectively becomes addition). For example, for the points A(2, 3) and B(1, 1), the distance is:
d = √[(1  2)² + (1  3)²] = √[9 + 16] = √25 = 5
.
By mastering Pythagoras’s theorem and correctly applying the formula, calculating the distance between two points on a straight line in a coordinate system becomes straightforward.