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A small problem with complex conjugations

  1. Jan 11, 2009 #1
    Hi!

    I have a problem with understanding an equation which is really simple.

    zz*=(a2+b2)

    shouldn't there be an i there if

    z1z2=(a1+ib1)(a2+ib2)

    is the equation correct?

    If it is could someone explain to me why there is no imaginary number?

    Thank You!
     
  2. jcsd
  3. Jan 11, 2009 #2
    if z = a + bi, then z* (conjugate of z) = a - bi so

    (z)(z*) = (a+bi)(a-bi) = a2 - (bi)2 = a2 -(i)2b2 = a2 -(-1)b2 = a2 + b2
     
  4. Jan 11, 2009 #3
    Yes I can see that now.

    Thanks!
     
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