For Education of Primary School

1. a
b
c
222
cba =+

2. Pythagorean Theorem Essential
Questions
How is the Pythagorean Theorem used to
identify side lengths?
When can the Pythagorean Theorem be
used to solve real life patterns?

3. This is a right triangle:

4. We call it a right triangle
because it contains a
right angle.

5. The measure of a right
angle is 90o
90o

6. The little square
90o
in the
angle tells you it is a
right angle.

7. About 2,500 years ago, a
Greek mathematician named
Pythagorus discovered a
special relationship between
the sides of right triangles.

8. Pythagorus realized that if
you have a right triangle,
3
4
5

9. and you square the lengths
of the two sides that make
up the right angle,
2
42
3
3
4
5

10. and add them together,
3
4
5
2
42
3 22
43 +

11. 22
43 +
you get the same number
you would get by squaring
the other side.
222
543 =+
3
4
5

12. Is that correct?
222
543 =+
?
25169 =+
?

13. It is. And it is true for any
right triangle.
8
6
10222
1086 =+
1006436 =+

14. The two sides which
come together in a right
angle are called

15. The two sides which
come together in a right
angle are called

16. The two sides which
come together in a right
angle are called

17. The lengths of the legs are
usually called a and b.
a
b

18. The side across from the
right angle
a
b
is called the

19. And the length of the
hypotenuse
is usually labeled c.
a
b
c

20. The relationship Pythagorus
discovered is now called
The Pythagorean Theorem:
a
b
c

21. The Pythagorean Theorem
says, given the right triangle
with legs a and b and
hypotenuse c,
a
b
c

22. then
a
b
c
.222
cba =+

23. You can use The Pythagorean
Theorem to solve many kinds
of problems.
Suppose you drive directly
west for 48 miles,
48

24. Then turn south and drive for
36 miles.
48
36

25. How far are you from where
you started?
48
36
?

26. 482
Using The Pythagorean
Theorem,
48
36
c
362
+ = c2

27. Why?Can you see that we have a
right triangle?
48
36
c
482
362
+ = c2

28. Which side is the hypotenuse?Which sides are the legs?
48
36
c
482
362
+ = c2

29. =+ 22
3648
Then all we need to do is
calculate:
=+12962304
=3600 2
c

30. And you end up 60 miles from
where you started.
48
36
60
So, since c2
is 3600, c is 60.So, since c2
is 3600, c is

31. Find the length of a diagonal
of the rectangle:
15"
8"
?

32. Find the length of a diagonal
of the rectangle:
15"
8"
?
b = 8
a = 15
c

33. 222
cba =+ 222
815 c=+ 2
64225 c=+ 2892
=c 17=c
b = 8
a = 15
c

34. Find the length of a diagonal
of the rectangle:
15"
8"17

35. Practice using
The Pythagorean Theorem
to solve these right triangles:

36. 5
12
c = 13

37. 10
b
26

38. 10
b
26
= 24
(a)
(c)
222
cba =+
222
2610 =+ b
676100 2
=+ b
1006762
−=b
5762
=b
24=b

39. Check It Out! Example 2
A rectangular field has a length of 100 yards and a
width of 33 yards. About how far is it from one corner
of the field to the opposite corner of the field? Round
your answer to the nearest tenth.

40. Check It Out! Example 2 Continued
11 Understand the Problem
Rewrite the question as a statement.
• Find the distance from one corner of the field to the
opposite corner of the field.
• The segment between the two corners is
the hypotenuse.
• The sides of the fields are legs, and they are 33 yards long
and 100 yards long.
List the important information:
• Drawing a segment from one corner of the field to the
opposite corner of the field divides the field into two
right triangles.

41. Check It Out! Example 2 Continued
22 Make a Plan
You can use the Pythagorean Theorem to
write an equation.

42. Check It Out! Example 2 Continued
Solve33
a2
+ b2
= c2
332
+ 1002
= c2
1089 + 10,000 = c2
11,089 = c2
105.304 ≈ c
The distance from one corner of the field to the
opposite corner is about 105.3 yards.
Use the Pythagorean Theorem.
Substitute for the known variables.
Evaluate the powers.
Add.
Take the square roots of both sides.
105.3 ≈ c Round.

43. The Pythagorean Theorem
“For any right triangle,
the sum of the areas of
the two small squares is
equal to the area of the
larger.”
aa22
+ b+ b22
= c= c22

44. Proof

45. a
a
a2
b
b
c
c
b2
c2
Let’s look at it
this way…

46. Baseball Problem
A baseball “diamond” is really a square.
You can use the Pythagorean theorem to find
distances around a baseball diamond.

47. Baseball Problem
The distance between
consecutive bases is 90
feet. How far does a
catcher have to throw
the ball from home
plate to second base?

48. Baseball Problem
To use the Pythagorean
theorem to solve for x,
find the right angle.
Which side is the
hypotenuse?
Which sides are the legs?
Now use: aa22
+ b+ b22
= c= c22

49. Baseball Problem
Solution
• The hypotenuse is the
distance from home to
second, or side x in the
picture.
• The legs are from home to
first and from first to
second.
• Solution:
x2
= 902
+ 902
= 16,200
x = 127.28 ft

50. Ladder Problem
A ladder leans against a
second-story window of a
house.
If the ladder is 25 meters
long,
and the base of the ladder
is 7 meters from the
house,
how high is the window?

51. Ladder Problem
Solution
• First draw a diagram that
shows the sides of the
right triangle.
• Label the sides:
– Ladder is 25 m
– Distance from house is 7
m
• Use a2
+ b2
= c2
to solve for
the missing side.
Distance from house: 7 meters

52. Ladder Problem
Solution
72
+ b2
= 252
49 + b2
= 625
b2
= 576
b = 24 m
How did you do?
A = 7 m