Which number is an irrational number?
a) �ã3 b) -13.5 c) 7/11
d) 1/ �ã9
What is the definition of an irrational number?
Since this is not my area of expertise, I searched Google under the key words "irrational number" to get these possible sources:
http://mathworld.wolfram.com/IrrationalNumber.html
http://en.wikipedia.org/wiki/Irrational_number
http://www.mathsisfun.com/irrational-numbers.html
http://mathforum.org/dr.math/faq/faq.integers.html
http://www.themathpage.com/aPreCalc/rational-irrational-numbers.htm
In the future, you can find the information you desire more quickly, if you use appropriate key words to do your own search.
I hope this helps. Thanks for asking.