## Introduction: Pythagorean Theorem

The name Pythagorean theorem came from a Greek mathematician by the named Pythagoras. Pythagoras developed a formula to find the lengths of the sides of any **right triangle**. Pythagoras Discovered that if he treated each side of a right triangle as a square (see figure 1) the two smallest squares areas when added together equal the area of the larger square. The formula is A2 + B2 = C2, this is as simple as one **leg **of a triangle squared plus another leg of a triangle squared equals the **hypotenuse **squared.

In this lesson I will teach you how to use the Pythagorean theorem, I will show where you put it to use and some different ways to use the theorem to find the lengths of legs when given the leg length and the hypotenuse length. I will try my best to explain every step of the way to my fullest and complete answer.

My inspiration for this instructable came from having the interest of finding how formulas work. I take interest especially in the Pythagoras theorem because we use it in lots of every day jobs such as engineering, woodworking and metalworking. I hope I can pass my interests on to you in this lesson.

Prescribed learning outcomes, by learning how the Pythagorean theorem works students will learn how to square, square root, add and subtract, and learn the Pythagoras formula.

Key words...**Hypotenuse- **In geometry, a hypotenuse is the longest side of a right-angled triangle, the side opposite the right angle.**Leg**- Either sides of a right triangle that are opposite to the hypotenuse.**Right triangle**- A triangle that has one corner of a ninety degree angle.

## Step 1: How to Use the Formula

Lets start with an example. If we know that leg A of the triangle is 3cm and leg B is 4cm the first step is **squaring** our legs. We can do this simply by multiplying one leg by same amount as its self, So therefore we get A = 9 and B = 16. The next step is adding we have to add both squared legs together to get one number witch in our case is 25. the final step is finding your **square root** of this final added number in this case is 5. Now that we have done every step we can come to the conclusion that the hypotenuse is 5cm.**Review,** in doing this equation is is extremely important that we follow all steps exactly. When learning the formula you have to have a basic understanding of three things, how to square, how to square root and how to tell which side is the hypotenuse. A little trick I use to find the hypotenuse is the two little lines that symbolize the ninety degree angle point to the hypotenuse.

Key words...**Squaring-** Squaring is the number you get when you multiply the number by it by its self.**square root- **A divisor of a quantity that when squared gives the quantity. For example, the square root of 25 is 5.

## Step 2: The Second Method

There are two methods in the theorem one you are given both the lengths of the legs and the other you are given the length of one leg and the hypotenuse. So for example our C side equals 12 and our B side equals 6. So if we know that C2 = 144 that means that A2 + B2 = 144 therefore 6 squared (36) plus B squared = 144. Now the next step is finding B2 the way you do that is to take both your known leg and the hypotenuse and subtract in our case we go B = 144 - 36 therefore B = 108.**review- **In this method we have to remember that we are trying to find a leg not the hypotenuse. We have to remember that instead of using the formula the way its written we have to order the steps differently, this order is C2 - B2 = A2.

Key words...**Hypotenuse**- The side opposite to the legs of the triangle( hint its the longest side)

## Step 3: Pythagorean Triples

A **Pythagorean triple **is any group of three** integer** values that satisfies the equation a2 + B2 = C2 is called a Pythagorean triple. therefore any triangle that has sides that form a Pythagorean triple must be a right triangle. When all three sides are **whole numbers** you have a Pythagorean triple*.* For example A = 3 B = 4 C = 5 this can also be called a 3,4,5 triangle. Here is how you do the equation for example 3 squared plus 4 squared = 5 squared, in other words 9 + 16 = 25 therefor because these are all whole numbers the triangle must be a Pythagorean triple.

There are four main **Pythagorean triples families** there is the 3,4,5, the 6,8,10, the 5,12,13, and the 8,15,17 triangles. If you multiply any of the three integers by the same amount you will still have a Pythagorean triple. For example 3,4,5, multiplied by two will give you 6,8,10, witch is a Pythagorean triple.**Review- **The integers represent the lengths of the sides of the triangles in a,b,c, order. If you do the equation and you don't come out with a whole number the integers are not a Pythagorean triple. Remember when multiplying Pythagorean triples families multiply all three numbers by the same amount.

Key words...**Pythagorean triple-**A right triangle where the sides are in the ratio of integers. (Integers are whole numbers like 3, 12 etc)**integer-**Includes the counting numbers {1, 2, 3, ...}, zero {0}, and the negative of the counting numbers {-1, -2, -3, ...}**Whole numbers-**There is no fractional or decimal part. And no negatives.

Example: 5, 49 and 980 are all whole numbers.**Pythagorean triples families-**every triple is a whole number multiple of the base triple.

## Step 4: Creat and Solve

Now using What you have just learned Cut out a A=5cm by B=12cm right triangle (don't forget to use a protractor to measure your angle) and try to figure out what side C equals. Put your answer in the comments if you like.

Now try to figure out a word problem...

If jimmy have a ladder leaning against a wall that is five feet in length, and the feet of the ladder are three feet away from the wall how far up the wall is the ladder? Feel free to answer in the comments below.**Practice questions...**

A = 6, B = ?, C =10

A = 5, B = 12, C = ?

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## 21 Comments

1 year ago

This really helped me out!

2 years ago on Step 3

Mispelled "which/witch"

And the a2+b2=c2 diagram has mis labeled in the a and b , "a," should be 16 not nine , "b" should be 9

5 years ago

does the Pythagorean theorem have 3 whole numbers? or the Pythagorean triple have 3 whole numbers? Can Pythagorean theorem have a non perfect whole number? or can Pythagorean triple have a non perfect whole number?

5 years ago

does the Pythagorean theorem have 3 whole numbers? or the Pythagorean triple have 3 whole numbers? Can Pythagorean theorem have a non perfect whole number? or can Pythagorean triple have a non perfect whole number?

10 years ago on Introduction

You mistake in the Pythaborean triples : You say there are four basic sets; that is not true there are an infinite set.

Secondly, you mention 3,4,5 (which is correct) followed by 6,8,10 which is no basic set (because all numbers are just the same multiple of 3,4,5).

A set could be 7,24,25 (you could take it as the third set).

There is a wiki about "formulas for generating pythgorean triples". (of which i derived the set here with the 7 ;)

One of the rules (from Euclides) :

-take an uneven number (a)

-square it. You get an uneven number.

-take the two concutive numbers that sum up to the square. These are b (the smallest, even) and c (de lagest, uneven).

Since there is an infinite set of prime numbers (who are no multiple of anything) to start with as a, this proves you have an infinite set of basic pythagorean triples.

Overall a nice instructable

Reply 6 years ago

exactly dude (6,8,10) is not a primitive pythagorean triplet)

6 years ago on Introduction

Here are some free printable worksheets that you can use for practice working with the Pythagorean theorem: http://stemsheets.com/math/pythagorean-theorem-worksheet

10 years ago on Introduction

Sorry to point this out, but in the first picture you describe the first triangle as A=3 and B=4, but in the second picture you describe it as A^2=16 and B^2=9. So I'm unsure if the two photographs are two different triangles, or if you made a mistake, but I think it would be less confusing if the two picture matched.

Reply 10 years ago on Introduction

Its all good i just put the picture for an example. Thanks anyway for the advise and don't forget to go vote for the cookie contest and the teacher contest

10 years ago on Introduction

In step 2 you subtracted 36 from 144 and gave 112 as the answer. That should be 108.

Reply 10 years ago on Introduction

Thanks so much that was a typo i'll fix it right away.

Reply 10 years ago on Introduction

All fixed!! Do you have any siggestions to make this ible better im trying to make it the best that it can be for the teacher contest!!

Thanks, cobalt420

Reply 10 years ago on Introduction

Ya I have a suggestion, you spell siggestions, suggestions....lol

~Mr. Mackenzie

Reply 10 years ago on Introduction

Teachable moments.

Dewey would be so jazzed by what just happened in this thread.

Reply 10 years ago on Introduction

What do you mean?

Reply 10 years ago on Introduction

John Dewey (of library organization fame) would have lauded you as an active learner. You are obviously putting in some great effort to win this contest, to the point of getting some math help and some English help. You're engaging in meaningful learning, and that learning is being assisted by a couple of awesome teachers.

And you're teaching in the process.

Pedagogical theory jokes. They are neither funny nor properly "jokes". I apologize for the confusion. Carry on being awesome.

Reply 10 years ago on Introduction

Thanks so much that really means alot and i' m really trying hard to win this contest.

Reply 10 years ago on Introduction

haha, i just learned this a couple weeks ago from my teacher! through he explained it a little differently...

10 years ago on Introduction

"We want teachers to show off the HANDS-ON projects they use with their students."

The above statement comes right from the contest description on the site. I recommend that you add a hands-on element to your lesson. Your steps are very thorough, but keep in mind that many students are kinesthetic learners, meaning they actually learn better by be being involved in a physical activity. Perhaps you could have students cut out or fold triangles as part of the lesson. Your lesson will be so much more effective if you come up with a creative gimmick.

Good Luck!

Reply 10 years ago on Introduction

Thank you so much I've made the change and even put in some practice questions.