Thursday, 18 May 2017

proof verification - Prove log46 is irrational

Thanks for taking the time to verify my approach and as well as my answer.



Background:





  • B.S. in Business from a 4-year university taking CS courses online

  • I would like some help with a basic proof from MIT's 6.042J Mathematics for Computer Science course.



The question is:
Prove log46 is irrational.



We prove the contradiction.





  • Suppose log46 is rational (i.e. a quotient of integers)
    log46=m/n

  • So we must have m, n integers without common prime factors such that
    4m/n=6

  • We will show that m and n are both even
    (4m/n)n=6n

  • So
    4m=6n


  • We then divide the two base numbers by their common factor, 2, which gives us:



2m=3n




  • Since the product of two even numbers must be even AND the product of two odd numbers must be odd, 2m and 3n are not equivalent and therefore m/n must not be rational.



Q.E.D. We conclude that log46 is irrational.

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