log 2 is irrational

       

        What is a rational number ?

 

                An rational number is a number, n, which can be written in the form

                               ,

        where p and q are integers, q ¹ 0 and the H.C.F. of p and q is equal to 1.

 

                In short, a rational number can be written in a fraction of two integers and an                      irrational number cannot.

 

 

        Short proof of “log 2 is irrational”

 

                Assume that log 2 is rational, that is,

                                         (1)

                where p, q are integers.

                Since log 1 = 0 and log 10 = 1,  0 < log 2 < 1  and therefore p < q.

                From (1),         

                                               

                                                   , where q – p is an integer greater than 0.

                Now, it can be seen that the L.H.S. is even and the R.H.S. is odd.

                Hence there is contradiction and  log 2  is irrational.

 

       

        For more serious learners

 

                Square root of 2 is also irrational. There are many proofs. You may study a few of         them by clicking here.