I'm having a bit of trouble proving the following property: Theorem If Re(z)>0 and Re(w)>=0, then log(zw)=log(z)+log(w), where log is the principal branch. I know that log(zw)=log(z)+log(w) mod 2pi i, but I am not really sure how that helps. Any thoughts?

Jaylyn Horne

Jaylyn Horne

Answered question

2022-10-17

Logarithm Propr
I'm having a bit of trouble proving the following property:
Theorem If R e ( z ) > 0 and R e ( w ) 0, then log ( z w ) = log ( z ) + log ( w ), where log is the principal branch.
I know that log ( z w ) = log ( z ) + log ( w )   m o d   2 π i, but I am not really sure how that helps. Any thoughts?

Answer & Explanation

erkvisin7s

erkvisin7s

Beginner2022-10-18Added 12 answers

Hint: Assume neither of z , w is 0. We can write z = r e i a , w = s e i b , with a ( π / 2 , π / 2 ) , b [ π / 2 , π / 2 ] . Then z w = ( r s ) e i ( a + b ) and a + b ( π , π ) .

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