The Pythagorean Theorem is a formula that gives a relationship between the sides of a right
triangle The Pythagorean Theorem only applies to RIGHT triangles. A RIGHT triangle is a
triangle with a 90 degree angle. The 90 degree angle in a right triangle is often depicted with a
square.
a c Pythagorean Theorem: a
2 + b2 = c2
b
NOTE: The side “c” is always the side opposite the right angle. Side “c” is called the
hypotenuse.
The sides adjacent to the right angle are named “a” and “b”.
There is no choice when selecting a side to be named “c”, but the sides you choose to call “a”
and “b” are interchangeable.
Example: Name each side of the triangle below. That is name one side a, one b and the
hypotenuse c.
The c is the side opposite the right angle. There is no flexibility when it comes to choosing the
side we name c.
The sides a, b are adjacent to the right angle and we have flexibility when naming them.
Each of these is a correct answer.
Answer 1: a = 3, b = 4 and c = 5
Answer 2: a = 4, b = 3, and c = 5
Example: Find the length of the missing side. Round to 2 decimals. Make sure to use the
proper units in your answer.
Step 1: Name each side. (It isn’t necessary to use the units (cm) until I write my answer.)
The side with the question mark is opposite the right angle. It needs to be called c.
The 2 and the 4 are the sides that need to be labeled a and b. I have a bit of flexibility.
It would be correct to call:
a = 2 and b = 4 or a = 4 and b = 2
I will pick a = 2 and b = 4
Step 2: put the values into the a2 + b2 = c2
formula and do the algebra to solve for the missing
side.
2
2 + 42 = c2
4 + 16 = c2
20 = c2
√20 = c
c = 4.47 cm
Example: Find the length of the missing side. Make sure to use proper units in your answer.
Step 1: Name each side. (It isn’t necessary to use the units (cm) until I write my answer.)
The side opposite the right angle is called c. c = 20
The side with the x and the 12 are the “a” and “b” for this problem. I will call a = 12 and
b = x
Step 2: Put the values into the a2 + b2 = c2
formula and do the algebra to solve for the missing
side.
122 + x2 = 20
2
144 + x2 = 400
-144 -144
x
2
= 256
x = √256
x = 16 cm
Example: Find the length of the missing side (round your answer to 2 decimals). Be sure to
include units in your answer.
Step 1: Name each side.
The side opposite the right angle is called c. c = 6.2
The x and the 4.9 are the sides for “a” and “b” in this problem. I will call a = 4.9 and
b = x
Step 2: put the values into the a2 + b2 = c2
formula and do the algebra to solve for the missing
side.
4.92 + x2 = 6.22
24.01 + x2 = 38.44
-24.01 -24.01
x
2
= 14.43
= √14.43
x = 3.798
x = 3.80 m
Step-by-step explanation: