
Number Theory Number Theory Math Forum 
 LinkBack  Thread Tools  Display Modes 
March 3rd, 2009, 12:55 PM  #1 
Newbie Joined: Feb 2009 Posts: 3 Thanks: 0  (x^2 = x * x) (x^0.5 = ??)
Help me! I know that the x^0.5 is the same as sqrt(x).. the square root of x... But my question is... if "x^2" is "x * x".. and "x^5" is "x * x * x * x * x".. What is "x^0.5" ?? How can one do "x * x" half a time?? I know I can solve the square root with the Babylonian method.. And I know stuff like that.. The only thing I am asking is. How can I do "x*x" half a time!?.. I mean "x^0.5"!?!? So... what is the proper definition of "x^0.5" ? This thing is driving me crazy! please help me!! Thanks! Cheers, Artheus 
March 3rd, 2009, 02:35 PM  #2 
Senior Member Joined: Feb 2009 From: Adelaide, Australia Posts: 1,519 Thanks: 3  Re: (x^2 = x * x) (x^0.5 = ??)
It's defined that way so that the rules of arithmetic are consistent. For whole numbers, it is clear that If you assume this rule holds for fractions as well, you find that . It turns out that this generalisation of the idea leads to consistent results, and so we can use it. You can even generalise further to irrational exponents by finding the limit of a sequence of approximating fractions. http://mathforum.org/library/drmath/view/65126.html One way of thinking about it is to say that if I start with the number 10 and "halfadd" 4, I get 12. If I "halfadd" 4 again, I get 14, which is the same as one whole addition of 4. If I start with the number 10 and "halfmultiply" 4, I get 20. If I "halfmultiply" 4 again, I get 40, which is the same as one whole multiplication by 4. The startingplace for addition is 0, and the startingplace for multiplication is 1. 
March 3rd, 2009, 03:08 PM  #3 
Global Moderator Joined: Nov 2006 From: UTC 5 Posts: 16,046 Thanks: 938 Math Focus: Number theory, computational mathematics, combinatorics, FOM, symbolic logic, TCS, algorithms  Re: (x^2 = x * x) (x^0.5 = ??)
I know 3 * 4 = 4 + 4 + 4, but what is 0.5 * 4? I know it's supposed to be equal to two by the rational multiplication formula, but how do I fill in the blank in "0.5 * 4 = 4 + ??"?

March 3rd, 2009, 03:28 PM  #4 
Member Joined: Jan 2009 Posts: 95 Thanks: 0  Re: (x^2 = x * x) (x^0.5 = ??)
I like this kind of questions because in mathematics, the most important thing, Iīts how you SEE things. x*x=x^2... but what happens if we dismantle this identity, and we ask for which number: y*y gives x... x^0.5*x^0.5 = x (you need to add the exponents) I think these things implies to see things from the image set instead of the origin set: thatīs inverse functions. I apologize if this is considered an stupidity. 