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Homework Help: Prove that e^ia + 2e^ib = re^ic?

  1. Jun 12, 2012 #1
    1. The problem statement, all variables and given/known data
    Prove that e^ia + 2e^ib = re^ic?

    2. Relevant equations
    given : r^2 = 5 + 4cos( a - b )
    tan c = (sin a + 2 sin b) / (cos a + 2 cos b)
    i is imaginary number

    3. The attempt at a solution
    I tried to expand e^ia + 2e^ib and make it equal to r^2
    but I dont know what to do with the tan c
  2. jcsd
  3. Jun 12, 2012 #2

    D H

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    Staff Emeritus
    Science Advisor

    What's wrong with arctangent?
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