Posted by Sanchia on Monday, June 15, 2009 at 11:10pm.
what are rational and irrational numbers??
i know that irrational numbers are numbers that cannot be expressed as a fraction, but i'm still confused.
there is this question:
which of the following are irrational numbers: √2, √8, 22/7, pi, 2√3
i know that 22/7 is rational, pi is irrational, but what about those square roots?

irrational numbers?!  drwls, Monday, June 15, 2009 at 11:49pm
Square roots of numbers that are not the squares of integers are all irrational. There is a way to prove that but I forgot the details. You have to assume that a fraction works and then prove that the assumption leads to a contradiction
Any number that does not meet the definition of being rational is irrational.

irrational numbers?!  Reiny, Tuesday, June 16, 2009 at 12:55am
 √2 is either rational or irrational.
 Assume that √ is rational so that
√2 = a/b, with a/b in lowest terms
 Square both sides to get
2 = a^2/b^2
then a^2 = 2b^2
 the right side of this equation is clearly an even number, since anything multiplied by 2 is even
 so a^2 must be even. We also know that if we square an odd number the result is odd, and if we square an even number the result is even
so a must be even
so a could be written as 2k
 rewriting our equation as
2b^2= (2k)^2
2b^2 = 4k^2
b^2 = 2k^2
by the same argument as above 2k^2 is even , so b has to be even
which means a and b are both even, therefore a/b is not in lowest terms
BUT that contradicts my assumption that a/b was a fraction in lowest terms
so √2 = a/b is a false statement
therefore √2 cannot be rational, and
must then be irrational
the same argument could be used for √3 and all other square roots

irrational numbers?!  brandy, Tuesday, September 1, 2009 at 4:55pm
true or false does this number represent a rational number 0.20200200020000200000

irrational numbers?!  Amber, Thursday, April 21, 2011 at 5:15pm
Is √4 Irrational?
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