No, 13 is not a rational number. Yes, here's the proof.
Let's start out with the basic inequality 9 < 13 < 16.
Now, we'll take the square root of this inequality:
3 < √13 < 4.
If you subtract all numbers by 3, you get:
0 < √13 - 3 < 1.
If √13 is rational, then it can be expressed as a fraction of two integers, m/n. This next part is the only remotely tricky part of this proof, so pay attention. We're going to assume that m/n is in its most reduced form; i.e., that the value for n is the smallest it can be and still be able to represent √13. Therefore, √13n must be an integer, and n must be the smallest multiple of √13 to make this true. If you don't understand this part, read it again, because this is the heart of the proof.
Readmore:http://wiki.answers.com/Q/Is_the_square_root_of_13_an_irrational_number#ixzz1WjS9rkGp
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The square root of 13 is irrational. All square roots of whole numbers are irrational unless the number is a perfect square.
169. 13 x 13 = 169. square root of 169 = 13.
It is both.13 is the square of +/- 3.6056, approx. However, since it is not the square of an integer, it is not a perfect square.It is also the square root of 169.
169
If the square root of a number is irrational, it is its own conjugate. sqrt(13)*sqrt(13) = 13 and you no longer have an irrational!