SOLUTION: Is the product if 2 complex conjugates always a real number? Explain by using a specific example, and a general example (x's and y's).

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Question 1007085: Is the product if 2 complex conjugates always a real number? Explain by using a specific example, and a general example (x's and y's).
Answer by ikleyn(52790) About Me  (Show Source):
You can put this solution on YOUR website!
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1) Is the product of 2 complex conjugates always a real number? 

   Yes, it is.


2) Explain by using a specific example

   Specific example: 

                     Let z = 3 + 4i. 
                     Then z%5Bconjugated%5D = 3 - 4i.
                     (3+4i)*(3-4i) = 3%2A3+%2B+cross%283%2A4%2Ai%29+-+cross%283%2A4%2Ai%29+-+4i%2A4i = 9+-+16%2A%28i%5E2%29 = 9 - 16*(-1) = 9 + 16 = 25.


3) Explain by using a general example (x's and y's):

                     Let z = x + yi. 
                     Then z%5Bconjugated%5D = x - yi.
                     (x+yi)*(x-yi) = x%2Ax+%2B+cross%28x%2Ay%2Ai%29+-+cross%28x%2Ay%2Ai%29+-+yi%2Ayi = x%5E2+-+y%5E2%2A%28i%5E2%29 = x%5E2+-+y%5E2%2A%28-1%29 = x%5E2+%2B+y%5E2.