Rational and irrational numbers explained with examples and non examples
Extending the classifications of numbers further, we encounter rational and irrational numbers. A rational number is a number that can be. Recognise and understand calculations which involve surds; Use surds in exact calculations; Recognise the difference between rational and irrational numbers. Common Core: 8th Grade Math Help» The Number System» Understand the Difference Between Rational and Irrational Numbers: cypenv.infotNS.
It is a number that cannot be written as a ratio of two integers or cannot be expressed as a fraction. For example, the square root of 2 is an irrational number because it cannot be written as a ratio of two integers.
Intro to rational & irrational numbers
The square root of 2 is not a number of arithmetic: Irrational numbers are square roots of non-perfect squares. Only the square roots of square numbers are rational.
Pi is an unending, never repeating decimal, or an irrational number.
The value of Pi is actually 3. Euler's Number e is another famous irrational number.
- Rational and Irrational Number
- Difference Between Rational and Irrational Numbers
- Rational and Irrational Numbers
Like Pi, Euler's Number has been calculated to many decimal places without any pattern showing. The value of e is 2. The golden ratio whose symbol is the Greek letter "phi" is also an irrational number. It is a special number approximately equal to 1. In all of these cases, these are all different representations of the number 1, ratio of two integers. And I obviously can have an infinite number of representations of 1 in this way, the same number over the same number.
And I could go on, and on, and on, and on.
Intro to rational & irrational numbers | Algebra (video) | Khan Academy
So negative 7 is definitely a rational number. It can be represented as the ratio of two integers. But what about things that are not integers? For example, let us imagine-- oh, I don't know-- 3. How can we represent that as the ratio of two integers? Or you could say, hey, 3. Or we could write this as negative 30 over negative 8. I just multiplied the numerator and the denominator here by negative 2.
But just to be clear, this is clearly rational. I'm giving you multiple examples of how this can be represented as the ratio of two integers. Now, what about repeating decimals?
Well, let's take maybe the most famous of the repeating decimals. Let's say you have 0. Or maybe you've seen things like 0.
Rational and Irrational Number
And there's many, many, many other examples of this. And we'll see any repeating decimal, not just one digit repeating. Even if it has a million digits repeating, as long as the pattern starts to repeat itself over and over and over again, you can always represent that as the ratio of two integers.
So I know what you're probably thinking. Hey, Sal, you've just included a lot. You've included all of the integers. You've included all of finite non-repeating decimals, and you've also included repeating decimals.
Are there any numbers that are not rational? And you're probably guessing that there are, otherwise people wouldn't have taken the trouble of trying to label these as rational. And it turns out-- as you can imagine-- that actually some of the most famous numbers in all of mathematics are not rational.