What is the difference between rational and irrational numbers?

In summary, the conversation discusses the classification of numbers as rational or irrational, specifically in decimal form. It is stated that a number is rational if it can be written as a fraction, and irrational if it cannot. The example of pi is given as an irrational number, while .66666... is rational because it can be expressed as a fraction. The concept of repeating decimals as a sign of rationality is also mentioned. The conversation briefly touches on the topic of irrational numbers in different integer bases, but it is stated that this is not possible.
  • #1
VashtiMaiden
31
0
Can someone pls help me on "rational and Irrational numbers". Esp. on Decimals. I can't classify if it is rational or irrational.
 
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  • #2
If you can write z = x/y where x and y are integers, then z is rational. Otherwise z is irrational.
 
  • #3
is pi rational?
 
  • #4
is .66666... rational? why?
 
  • #5
Is Pi rational? No. Not sure how to prove it though.
Is .66666... rational? Can you think of a fraction that gives .666666... ? I would hope you can.
 
  • #6
ok, thanks nicksauce
 
  • #7
for decimal form a useful fact is
a real nummber x is rational if and only if its decimal expansion at some point repeats.
let () be repeat this sequence
1/9=.(1) so rational
8134808921309.2872918752801(29148991280409) so rational

pi has no such patern, though this is not obvious
 
  • #8
ah, ok,
 
  • #9
lurflurf said:
for decimal form a useful fact is
a real nummber x is rational if and only if its decimal expansion at some point repeats.

Little off-topic, but here goes: I'm curious, is this not true in some integer base?
 
  • #10
If you mean "is it true in any integer base", yes.
 
  • #11
The question has been answered, but maybe I can help you grasp this a little easier. "Irrational" means that it cannot be expressed as a ratio (NOT that it is 'irrational' in the sense of not being reasonable.) Hence "irrational," or "un-ratio-expressable" if you will. A rational number, on the other hand, CAN be expressed as a ratio. It's "rational," or "ratio-expressable." Since a repeating decimal is given by the 'ratio' of two numbers, it is indeed rational (i.e. 'expressable as a ratio.')
 
  • #12
JohnDuck said:
Little off-topic, but here goes: I'm curious, is this not true in some integer base?

Sorry no
in base pi
pi which is irrational=10
4 which is rational=10.220122021

a problem with algebraic bases
in base root-2
root 2=10
2=100
 
  • #13
Did you miss the word "integer" in "integer base"?
 

What is the difference between rational and irrational numbers?

Rational numbers are numbers that can be expressed as a ratio of two integers, while irrational numbers cannot be expressed as a ratio and have non-repeating, non-terminating decimal expansions.

How can you determine if a number is rational or irrational?

A number can be determined to be rational or irrational by trying to express it as a fraction. If it can be written as a fraction, then it is rational. If not, then it is irrational.

Are all square roots irrational numbers?

No, not all square roots are irrational numbers. Some square roots, such as the square root of 4, can be expressed as rational numbers.

Why are irrational numbers important in mathematics?

Irrational numbers are important in mathematics because they help to bridge the gap between rational numbers and real numbers. They allow for more precise calculations and help to explain certain mathematical concepts.

Can irrational numbers be approximated?

Yes, irrational numbers can be approximated by rounding the decimal representation to a certain number of digits. However, the approximation will never be exact since irrational numbers have infinite non-repeating decimals.

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