Math Proof

If c is rational, c does not = 0, and x is irrational, then cx and c+x are irrational.

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asked by Ashley
  1. sum:
    Assume that it is rational. That is, if c = a/b, then

    a/b + x = m/n
    for some integers m and n.

    That means that

    x = m/n - a/b
    But m/n-a/b = (bm-an)/(bn), clearly a rational number, and x is irrational.

    So, if x is irrational, c+x cannot be rational.

    Clearly, cx must also be irrational, since multiplication is just a shorthand for addition. You can prove it in the same way as the sum. Assume cx is rational and show that it cannot be.

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    posted by Steve
  2. Thank you!

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    posted by Ashley

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