Let's look at what makes a number rational or irrational ...
Rational Numbers
A Rational Number can be written as a Ratio of two integers (ie a simple fraction).
Example: 1.5 is rational, because it can be written as the ratio 3/2
Example: 7 is rational, because it can be written as the ratio 7/1
Example 0.333... (3 repeating) is also rational, because it can be written as the ratio 1/3
Irrational Numbers
But some numbers cannot be written as a ratio of two integers ...
...they are called Irrational Numbers.
Example: π (Pi) is a famous irrational number.
Pi
π = 3.1415926535897932384626433832795... (and more)
We cannot write down a simple fraction that equals Pi.
The popular approximation of 22/7 = 3.1428571428571... is close but not accurate.
Another clue is that the decimal goes on forever without repeating.
Cannot Be Written as a Fraction
It is irrational because it cannot be written as a ratio (or fraction),
not because it is crazy!
So we can tell if it is Rational or Irrational by trying to write the number as a simple fraction.
Example: 9.5 can be written as a simple fraction like this:
9.5 =
19
2
So it is a rational number (and so is not irrational)
Here are some more examples:
Number As a Fraction Rational or
Irrational?
1.75
7
4
Rational
.001
1
1000
Rational
√2
(square root of 2) ? Irrational !
Square Root of 2
Let's look at the square root of 2 more closely.
square root 2When we draw a square of size "1",
what is the distance across the diagonal?
The answer is the square root of 2, which is 1.4142135623730950...(etc)
But it is not a number like 3, or five-thirds, or anything like that ...
... in fact we cannot write the square root of 2 using a ratio of two numbers
... I explain why on the Is It Irrational? page,
... and so we know it is an irrational number
Famous Irrational Numbers
Pi
Pi is a famous irrational number. People have calculated Pi to over a quadrillion decimal places and still there is no pattern. The first few digits look like this:
3.1415926535897932384626433832795 (and more ...)
e (eulers number)
The number e (Euler's Number) is another famous irrational number. People have also calculated e to lots of decimal places without any pattern showing. The first few digits look like this:
2.7182818284590452353602874713527 (and more ...)
phi
The Golden Ratio is an irrational number. The first few digits look like this:
1.61803398874989484820... (and more ...)
radical symbol
Many square roots, cube roots, etc are also irrational numbers. Examples:
√31.7320508075688772935274463415059 (etc)
√999.9498743710661995473447982100121 (etc)
But √4 = 2 (rational), and √9 = 3 (rational) ...
... so not all roots are irrational.
pls, branliest :)
