# Pythagorean Theorem: The Theory of Pythagoras and How it Works

In school we tend to think that the Pythagorean theorem is just another stupid geometry problem that teachers throw at us. It's yet **another** headache that math gives us (as if we needed any more hard school subjects). And it's useless! All it does it solve a triangle's sides. Big whoop. Now I can figure out the dimensions of my triangular-shaped dog, Tripoodle.

Oh, but the Pythagorean theorem has many more uses apart from solving the dimensions of geometrically awkward animals. Read on to find out.

## What is it?

The Pythagorean theorem, or Pythagoras' theorem, is a relationship between the sides of a **right angle** (90 degree) triangle.

It's written as an equation:

a^{2} + b^{2} = c^{2}

Where **a**, **b** and **c** are the sides of a triangle, c being the side opposite to the 90 degree angle. It is also the longest side in a right triangle, known as a **hypotenuse**. The other sides, "a" and "b", are known as the **legs** or the **catheti**.

## Right Angle Triangle

The right angle is denoted by the square shape in the angle **C**.

Angles **A** and **B** are **acute angles** - their values are less than 90 degrees.

In contrast, **obtuse angles** are angles with values greater than 90 degrees. There are no obtuse angles in right angle triangles.

This is all very dry and technical, but bear with me! There's some fun stuff up ahead!

## How can you prove it?

There are many ways to prove the Pythagorean theorem. The book *Pythagorean Proposition*, by Elisha Scott Loomis, has 367 different ways of proving it.

Here is a great Hub that has a very simple and creative solution for the theorem. Don't get overwhelmed by the diagrams! It's actually very easy to understand.

## But how do you solve a Pythagorean problem?

As long as you have two sides of a triangle, you can solve the remaining one using the formula.

a^{2} + b^{2} = c^{2}

The only tricks here are that you have to identify which side is "c" or the hypotenuse, what sides you are given, and which side you are looking for.

## Example 1 - Solving for Hypotenuse

## How about a few examples?

To the side is a right angle triangle with an unknown variable "x". Now how do we go about solving this problem?

**Step 1: **Find out what information you are given.

We are given the length of two sides of the triangle, 3 and 4. We also know that it's a right angle triangle because of its 90 degree angle (shown by the square drawing).

**Step 2****:** Identify the hypotenuse.

In this case, the hypotenuse is "x"; we know this because "x" is the longest side of the triangle and that it's opposite of the right angle.

This means that in the formula a^{2} + b^{2} = c^{2}, the "x" value is the "c" value. It's given a different letter, but it means the same thing. It's just a variable for the hypotenuse.

This also means that the other two values, 3 and 4, that were given to us are the legs "a" and "b" in the formula. It doesn't really matter which is which, it'll turn out the same.

**Step 3****: **Solve the equation!

Since we're looking for the hypotenuse "c", which is "x" in the diagram, and we're given 3 and 4 as "a" and "b" in the formula, we have everything we need to solve!

So writing it out:

(3)^{2} + (4)^{2} = x^{2}

^{Now we expand the brackets by squaring the numbers:}

9 + 16 = x^{2}

We simplify that into:

25 = x^{2}

And finally, we take the square root of the result:

x = 5

It's as easy as that! The hypotenuse of this triangle is 5.

## Example 2 - Hypotenuse Given

## How about another example?

Ok, this seems pretty straightforward, but it looks like we're given different values. Let's go through the steps to figure it out!

**Step 1:** Find out what information you are given.

We are given the length of two sides of the triangle, 10 and 6. And again, we know it's a right angle triangle because of the "square" diagram (it means it's **perpendicular** i.e. that it makes a right angle).

**Step 2****: **Identify the hypotenuse.

In this case, the hypotenuse is 10; we know this because 10 is the longest side of the triangle and that it's opposite of the right angle.

This means that in the formula a^{2} + b^{2} = c^{2}, the value 10 is the "c" variable.

This also means that the other value we're given, 6, is either "a" or "b". Again, it doesn't matter which.

Now we know that we're solving for one of the missing legs of the triangle. This is also given the variable "x" in the diagram.

**Step 3****:** Solve the equation!

Since we're looking for the leg "x" and we're given10 as "c" and 6 as "a" (or "b") in the formula, we have everything we need to solve!

Writing it out:

x^{2} + (6)^{2} = (10)^{2}

^{Now we expand the brackets by squaring the numbers:}

x^{2} + 36 = 100

Now we rearrange the equation:

x^{2} = 100 - 36

Simplify it:

x^{2} = 64

And finally, we take the square root of the result:

x = 8

There we go! The missing "leg" of this triangle has a value of 8, the other "leg" is equal to 6, and the hypotenuse is equal to 10.

Wait a minute! That sounds oddly *similar*...

Look at our previous example - it has side values of 3, 4 and 5. Our second example has values of 6, 8 and 10. Our second triangle is just like our first triangle, but with all of its dimensions doubled!

These two triangles are known as **similar triangles** - they have the same shape, and they can scale up! You can shrink or expand each side by the same amount, and it'll look the same.

## Ok I know how to use it, but what are some of its applications?

You mean other than figuring out the length of your Tripoodle's hypotenuse?

There are quite a few uses for the Pythagorean theorem. Construction, architecture and engineering have some common uses from the formula. It also comes useful in some physics problems, like vectors in kinematics and force/motion problems.

It's also a stepping stone to some of the more difficult mathematic problems. On this principle, you build up or combine it with more techniques like trigonometry.

The Pythagorean theorem is actually a special case of the cosine law, which applies to all triangles. This will be covered in a separate article.

Now why don't you get some practice with the following questions?

## Question 1

## Question 2

## Question 3

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## Comments 22 comments

Tripoodles are an endangered species..I have only seen one or two in my lifetime

It was fun learning Pythagorean here. As a teacher I also give this method for my student. Thank you very much, my friend. I rate this and thumbs Up.

I can't believe somebody just wrote 4 screens about Pythagorean triangles! Whom is this being aimed at? Grade 5 pupils?

I'm afraid that if one can't understand triangles then they should start taking more art classes because any technical subject is obviously not going to be their cup of tea.

With so many excellent tutorials online (including videos) there's today really no excuse not to understand anything that's being taught up to Grade 12.

Maybe less Facebook and more Google is what kids today need.

Only after I had posted my rant (yes, it was a rant) I noticed this is your first week. Sorry for being too harsh.

I just don't get how ANYBODY beyond Grade 9 doesn't know Pythagorean theorem. It's something as fundamental as using a spoon to feed oneself.

When I said "to use more Google" what I meant was to use Google to find the excellent tutorials on anything a person doesn't know.

A good book on anything concerning Euclidean geometry is Euclid's book called "Elements" written 2,000+ years ago: http://en.wikipedia.org/wiki/Euclid%27s_Elements

I'm eager to see what you're about to write about kinematics and vectors (OK, I'll admit it -- I wasn't very good in solving partial differential equations of functions of more variables in POLAR coordinates).

Wow, great explanation! When I first saw your hub title I had flashbacks of math class. I would still consider this knowledge to be helpful for people over grade 9. Why? Because a lot of people who have been out of school for years and need to figure this out and just don't remember would find this useful. I think a lot of people even though they've had advanced math classes in school don't remember every thing that they were taught, even if it's easy and simple for some people out there.

Blargh. Despite my ability to understand mathematical concepts and figure stuff out like how long it would take a train to get to x place at y speed...I hate math. And I hate geometry more.

I do possess the mental facilities to visualize (obviously, being a writer) but I don't have the patience.

But ohh, do I love quantum mechanics. And mechanics, in general. I used to watch a PBS series on it, when I was up late enough to happen by it. Fun stuff.

--guess I do well if I see the applications for it.

But the Pythagorean theorem is as basic as you get...ahh, enough of my ranting. ;)

I felt I needed to tell you after reading your comments that I myself learned this stuff in the 9th grade, however I am now in college and needed help re-jogging my memory as I now work on college math. Your page was so helpful, and really helped me re-teach myself this matter. I am thankful that there are people like you out there who makes these pages which can be so useful in life.

This hub is done very well. Even though I learned all this in high school, there is nothing wrong with reviewing the information. You also provide definitions and hint at more advanced topics. The Tripoodle is too cute.

Hi mrpopo, just wanted to say thanks for this Hub, I think it's great when people post articles like these - I have found it really useful as I needed to revise for a maths test on various topics and my mind just went blank when it came to Pythagoras Theorem! Thanks to your well explained Hub, I passed all three questions above after having to practically teach myself Pythagoras again! Thanks, and I look forward to using more of your Hubs to teach myself other math techniques that I have forgotten! :)

Hello everyone,

I would be conducting a seminar in my University on How to apply Pythagoras theorem in our practical life, professions and business, please if you have any information that can help, you can contact or send it to eakande36@yahoo.com

This was amazing its explained better here I even got full marks for my pythagoras assignment thanks this was amazing

This was amazing its explained better here I even got full marks for my pythagoras assignment thanks this was amazing

A wonderful job. Super helpful inotomarifn.

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