Amy Hatfield Central High School The Distance Formula A(-4, 3) B(8, -5) Amy Hatfield Central High School
Finding the length of vertical or horizontal segments in the coordinate plane is simple: just count the number of blocks from one endpoint to the other! A B X Y AB = 8 units XY = 7 units
What do you do if the segment isn’t horizontal or vertical What do you do if the segment isn’t horizontal or vertical? You can’t count blocks! ? ? D(3, 2) C(-2, -1)
Let’s use our geoboards to model this situation Let’s use our geoboards to model this situation. We can form a right triangle with the segment CD as the hypotenuse. D C
Let’s use the Pythagorean Theorem to find the length of segment CD. 3 units C 5 units a2 + b2 = c2 52 + 32 = c2 25 + 9 = c2 c2 = 34 c =34 5.83 units
The number 5 came from the positive difference between the two x coordinates, x1 and x2. Likewise, the number 3 came from the positive difference between the two y-coordinates, y1 and y2. D(x2, y2) C(x1, y1)
This is the distance formula!! Now, using the Pythagorean Theorem, plug in the variables instead of the numbers. c2 = a2 + b2 d2 = (x2 – x1)2 + (y2 - y1)2 d = (x2 – x1)2 + (y2 - y1)2 This is the distance formula!!