



 
Nazrul, I see nothing wrong at all in your proof. It appears to me to be complete for the set of complex numbers. There are a number of ways of proving this and your method is a good one. The teacher who said your "process is wrong" must want you to use a different (particular) method, but the method you have used is also valid. You will have to ask the teacher which process he or she wants you to use instead. Cheers,  


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