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Homework Help: How is sinx/(2sin(x/2)) = cos(x/2)?

  1. Oct 9, 2012 #1
    1. The problem statement, all variables and given/known data
    Prove sinx/(2sin(x/2)) = cos(x/2)
    (sin(x) cos(x/2^(n+1)))/(2^n(sinx/2^n)) = sinx/(2^(n+1)sin(x/(2^n+1)))

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Oct 9, 2012 #2


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    For the first, how do you expand [itex]\sin(2x)[/itex] into terms of sin(x) and cos(x)? Now apply that to the numerator sin(x).

    For the second, again apply the same rule.
  4. Oct 9, 2012 #3


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    Hello mr0no. Welcome to PF !

    According to the rules for homework help in this Forum, you need to show your work before we can help.

    Since you're new here, I'll give you a hint.

    For the first one use the double angle identity to write sin(x) in a different manner, by looking at sin(x) as sin(2(x/2)) .
  5. Oct 9, 2012 #4
    Thanks for giving me a tip instead of solving the whole thing for me. That's just what I need. I guess I will be revising trig identities tomorrow :)
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