Friday, 27 February 2015

Valid proof by induction for modulus of a product of complex numbers



I want to prove that |z1z2z3zn|=|z1||z2||z3||zn|



Now this really feels like something I can just throw induction at.




Base case: n=2.



|z1z2|=|z1||z2| follows directly from expressing these numbers in exponential form.



Induction hypothesis:



Now assume that for k, we can say that



|z1z2z3zk|=|z1||z2||z3||zk|.




Inductive step:



Call the product of the first terms w



|z1z2z3zkzk+1|=|w zk+1|=|w||zk+1|



Now use the induction hypothesis:



|w||zk+1|=|z1||z2||z3||zk||zk+1|.




The aforementioned theorem holds by the principle of induction. QED



Modulus really feels like a homomorphism like this, did I do my proof correctly, should I elaborate? Is my writing clear? Any tips or recommendations? I really feel induction proofs are a bit rigid sometimes, the interesting ones are the ones where the inductive step isn't straightforward at all and requires some extra skill or inspiration.


Answer



Your solution is perfect. There is nothing to add. Perhaps only this for n=2:



|zw|=zw¯zw=z¯zw¯w=|z||w|


No comments:

Post a Comment

real analysis - How to find limhrightarrow0fracsin(ha)h

How to find lim without lhopital rule? I know when I use lhopital I easy get $$ \lim_{h\rightarrow 0}...