Return to the Purplemath home page

 The Purplemath Forums
Helping students gain understanding
and self-confidence in algebra


powered by FreeFind

 

Return to the Lessons Index  | Do the Lessons in Order  |  Get "Purplemath on CD" for offline use  |  Print-friendly page

The Distance Formula (page 1 of 2)


The Distance Formula is a variant of the Pythagorean Theorem that you used back in geometry. Here's how we get from the one to the other:

 

Suppose you're given the two points (2, 1) and (1, 5), and they want you to find out how far apart they are. The points look like this:

  

 plotted points

  

 

You can draw in the lines that form a right-angled triangle, using these points as two of the corners:

  

 right triangle

  

 

It's easy to find the lengths of the horizontal and vertical sides of the right triangle: just subtract the x-values and the y-values:

  

 lengths
   

Then use the Pythagorean Theorem to find the length of the third side (which is the hypotenuse of the right triangle):

    c2 = a2 + b2

...so:   Copyright Elizabeth Stapel 2000-2011 All Rights Reserved

    c = 5

This format always holds true. Given two points, you can always plot them, draw the right triangle, and then find the length of the hypotenuse. The length of the hypotenuse is the distance between the two points. Since this format always works, it can be turned into a formula:

    Distance Formula: Given the two points (x1, y1) and (x2, y2), the distance between these points is given by the formula:

Don't let the subscripts scare you. They only indicate that there is a "first" point and a "second" point; that is, that you have two points. Whichever one you call "first" or "second" is up to you. The distance will be the same, regardless.

  • Find the distance between the points (2, 3) and (4, 4).

    I just plug the coordinates into the Distance Formula:

      d = sqrt(53)

    Then the distance is sqrt(53), or about 7.28, rounded to two decimal places.

Top  |  1 | 2  |  Return to Index  Next >>

Cite this article as:

Stapel, Elizabeth. "The Distance Formula." Purplemath. Available from
    http://www.purplemath.com/modules/distform.htm. Accessed
 

 



Purplemath:
  Linking to this site
  Printing pages
  School licensing


Reviews of
Internet Sites:
   Free Help
   Practice
   Et Cetera

The "Homework
   Guidelines"

Study Skills Survey

Tutoring from Purplemath
Find a local math tutor


This lesson may be printed out for your personal use.

Content copyright protected by Copyscape website plagiarism search

  Copyright 2000-2012  Elizabeth Stapel   |   About   |   Terms of Use

 

 Feedback   |   Error?