Topic: the distance between two points.
P (x ,y )
The distance between P and Q ( PQ ) is
(x 2 −1 )2 +y 2 − 1 )2
x ( y
Example: Find the distance between the points with
coordinates (-3,4) and (5,-3).
Solution: ( (−3) − 5) 2 + ( 4 − (−3) ) 2 = 64 + 49 = 113 ≈ 10.6
Find the distance between the points with coordinates (-3,4)
STEP 1: Draw the situation! (The situation will get more
0 1 x
STEP 2: So, what do you think the distance between the two
points will be? 3? Or 5? Or greater ? Why?
STEP 3: We are going to find out. We will use a right
triangle, and Pythagorean theorem.
0 1 x
Recall:Pythagorean Theorem for the right triangle above:
• What is the distance between A and B? (You can just
count: 8) (USE OF COMMON SENSE, OF WHAT YOU
(If you want to express it already in terms of the x-coordinates: |
5-(-3)|=8; but maybe better to first show that you don’t need any
• What is the distance between A and C? (You can just
count: 7) (USE OF COMMON SENSE, OF WHAT YOU
(If you want to express it already in terms of the y-coordinates: |
(-3)-4|=7; but maybe better to first show that you don’t need any
• So what is the distance between B and C? With use of
(BC)2= 82+72 = 64+49 = 113, so the distance between B and C
is 113 = 10.6
STEP 4: From your first estimation and the drawing, you
think 10.6 could be the correct answer? So you did not make
After this, you can give one other example, or you can
already let them work. You could even ask the students to
give a general formula of the distance between two points, if
they have practised enough exercises.
You can also ask a CONTEXT-problem in which distance is
concerned, for instance:
Mark lives 3 km from school and Rona lives 5 km from
a) What is the maximum possible distance between their
two houses and what is the minimum possible distance
between their two houses?
b) If the situation is as illustrated below, how far do Mark
and Rona live apart?
c) If you know that Rona and Mark live 4 km apart, draw in
the graph below the possible locations for Mark’s
How did you find the locations?