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What is wrong here?

  1. Feb 15, 2013 #1
    I'm given the fact that exp(y) ≥ 1 + y for all y

    I will use this for sinh. Since sinh = (exp(y) - exp(-y))/2 we have for y=3 as example:

    sinh(3) ≥ 3 by subtracting the two inequalities

    Instead for sinh(-3) I get:

    sinh(-3) ≥ -3 (1)

    But something is wrong here: Because if I take the first inequality sinh(3) ≥ 3 and multiply it by (-1) and switch around the inequality sinh and using the fact that
    -sinh(3) = sinh(-3) I get:

    sinh(-3) ≤ -3 (2)

    This is clearly weird. Which of (1) and (2) is right and why is other one wrong?
     
  2. jcsd
  3. Feb 15, 2013 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Careful when subtracting inequalities:

    5 > 3
    4 > 1

    subtracting:
    1 > 2 ???
     
  4. Feb 15, 2013 #3
    ahh omg. Thanks LOL
     
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