Complex Numbers


   
 
De Moivre's Theorem
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Statement of DeMoivre's Theorem
 
If 'n' be any rational number, positive or negative, then
 
 
Proof:
 
Part I: When 'n' is any integer, positive or negative then
 
 
 
Part II: When 'n' is a fraction.
 
Part I:
 
Case 1:
 
When n is a positive integer.
 
By actual multiplication, we have
 
 
 
 
 
 
 
 
Similarly by the method of induction,
 
 
 
 
Case 2:
 
When 'n' is a negative integer.
 
Let n = -m and m > 0
 
 
 
 
 
 
 
 
 
 
 
Part II:
 
Case 3:
 
When 'n' is a fraction.
 
 
 
where 'p' is any positive integer and 'q' is any integer.
 
From Part I,
 
 
 
 
Now taking qth root of both sides,
 
 
 
 
 
 
 
Hence the theorem.
 
Corollary 1
 
 
 
 
 
Corollary 2
 
 
 
 
Corollary 3
 
 
 
     
   
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