1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Elementary math proof

  1. Apr 30, 2016 #1
    1. The problem statement, all variables and given/known data
    Proof 2/5*(2^0.5)-1/7 is irrational

    2. Relevant equations


    3. The attempt at a solution
    I did this by splitting the expression and setting contradictions
    2/5->rational
    2^0.5->irrational

    Proof first rational times irrational is irrational

    Proof by contradiction

    Assume the product is rational
    let rational be x/y irrational s and the product u/t

    rational*irrational=x/y*s=u/t
    s=uy/tx

    Contradiction s can't be rational

    and then I do the same thing for irrational-rational

    Is that the right approach?
     
  2. jcsd
  3. Apr 30, 2016 #2

    Ken G

    User Avatar
    Gold Member

    Sure-- a proof is a proof, and that would prove it. The question I have is if you are allowed to take as given that the square root of 2 is irrational, but if you are, proof by contradiction is certainly the way to go.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Elementary math proof
  1. Math series proof (Replies: 2)

Loading...