Download Pythagorean Theorem

Pythagorean Theorem
CC.2.3.8.A.3 - Apply the Pythagorean
Theorem to determine
unknown side lengths in right triangles in realworld and mathematical problems in two and
three dimensions.
MATH 8
Bell Ringer
Solve for x
• x2+7=43
• 64+x2=164
Evaluate for a = 12, b = 5, c = 13
3. a2 + b2
4. c2 – b2
Objective
We are going to learn about the
Pythagorean Theorem.
We are going to learn how to use
the Pythagorean Theorem to solve for a
missing length of a right triangle.
Pythagorean Theorem
• What is the Pythagorean Theorem in
symbol form?
2
a
+
2
b
2
c
=
• Which of these variables represent the
hypotenuse?
c
• Once you have figured out which is c,
does it matter which leg is a and which
is b?
no
Steps to Solve for a missing side
of a right triangle using the
Pythagorean Theorem
Step 1: Write the formula
Step 2: Substitute known values for the
variables.
Step 3: Solve the equation for the missing
variable.
Example 1
Find x
8 ft
x
15 ft
• Step 1: Write the formula
a2 + b2 = c2
• Step 2: Substitute known values 82 + 152 = c2
Which number goes where?
You need to identify the hypotenuse. (It’s the one opposite of
the right angle.)
The hypotenuse is always the c in the formula. We do not know
the value of c, so it stays as c in the formula.
Does it matter whether we use a = 8 or 15? No.
Let’s use a = 8 and b = 15.
Example 1
Find x
x
8 ft
15 ft
• Step 1: Write the formula
a2 + b2 = c2
• Step 2: Substitute known values 82 + 152 = c2
• Step 3: Solve for the missing variable, in this case c.
We are not done yet…
We have found c2, but
not just plain c.
We were told to solve for x, not c.
So we should replace the c with an x.
64 + 225 = c2
289 = c2
289 = c2
17 = c
x = 17
YOU TRY
Find x
5 ft
x
12 ft
52 + 122 = x2
25 + 144 = x2
169 = x2
• Answer:
x = 13
Example #2
Find x.
14 in
x
Round to the nearest
hundredth.
6 in
• Step 1: Write out the formula
• Step 2: Substitute known values
a2 + b2 = c2
a2 + 62 = 142
Which number goes where?
This time we are given the hypotenuse. So, c = 14
Does it matter whether we use a = 6 or b = 6?
Let’s use b = 6.
No
Example #2
Find x.
14 in
x
Round to the nearest
hundredth.
6 in
• Step 1: Write out the formula
• Step 2: Substitute known values
• Step 3: Solve for the missing variable.
Can we just add the two numbers and do
the square root?
No, they are not on
the same side of the equals sign.
x = 12.65
a2 + b2 = c2
a2 + 62 = 142
a2 + 36 = 196
– 36 – 36
a2 = 160
a2 = 160
a = 12.64911
What is the difference between
the 2 examples?
• Both have us squaring the given sides.
• Both have us using the square root at the
end.
• The only difference is in the middle.
– Example 1 has us adding the numbers
– Example 2 has us subtracting the smaller from
the larger.
What does this mean?
• When you have two sides of a right triangle,
you can find the third using the Pythagorean
Theorem.
• Square both of the measurements you have.
• Add or subtract the two numbers depending
on whether or not you have the hypotenuse.
(Subtract if you have it, add if you don’t)
• Find the square root of the result and you
have your missing side!
Try this one.
x
15
20
Solve for x.
Round your answer to the nearest hundredth if necessary.
Answer:
Try this one.
7
12
x
Solve for x.
Round your answer to the nearest hundredth if necessary.
Answer:
Try this one.
5
x
3
Solve for x.
Round your answer to the nearest hundredth if necessary.
Answer:
Try this one in your notes…
30
7
x
Solve for x.
Round your answer to the nearest hundredth if necessary.
Answer:
Try this one.
b
a
c
If the hypotenuse of this triangle is 10 and a is 6 which
equation would you use to find b?
a) 6 + b = 10
b) 36 + b = 100
c) b2 – 36 = 100
d) 36 + b2 = 100
Answer: