I made a mistake with e e in C \mathbb{C} , but I ammended it

Calculus Level 4

True or false ? (In C \mathbb{C} ) lim z 0 ( e z ) 1 z = e \displaystyle \lim_{z \to 0} (e^{z})^{\frac{1}{z}} = e

Note.- We are using the exponentiaton complex, and not the multivalued function or multifunction " exp(z) \text{ exp(z)} " ,i.e, if h : C { 0 } C h : \mathbb{C} - \{0\} \longrightarrow \mathbb{C} is the function h ( z ) = ( e z ) 1 z h(z) = (e^{z})^{\frac{1}{z}} then lim z 0 h ( z ) = e , is true or false ? \displaystyle \lim_{z \to 0} h(z) = e, \text{ is true or false ?} Bonus.- what about lim z 0 ( e 1 z ) z = e \displaystyle \lim_{z \to 0} (e^{\frac{1}{z}})^{z} = e ?

False This limit doesn't exist in C \mathbb{C} True Undecidable

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

1 solution

( e z 1 + z e^z \sim 1 + z , as z 0 z \to 0 ), and ( ln ( 1 + z ) z \ln (1 + z) \sim z , as z 0 z \to 0 ), so lim z 0 ( e z ) 1 z = lim z 0 ( e 1 z ( ln ( 1 + z ) ) ) = lim z 0 e ( 1 z z ) = e \displaystyle \lim_{z \to 0} (e^{z})^{\frac{1}{z}} = \lim_{z \to 0} (e^{\frac{1}{z} (\ln (1 + z))}) = \lim_{z \to 0} e^{(\frac{1}{z} \cdot z)} = e What about the bonus ? Warning: You can't use my previous argument .

Bonus . lim z 0 ( e 1 z ) z = lim z ( e z ) 1 z \displaystyle \lim_{z \to 0} (e^{\frac{1}{z}})^{z} = \lim_{z \to \infty} (e^z)^{\frac{1}{z}} This limit doesn't exist in C \mathbb{C} , because if R R , R > 0 R \in \mathbb{R}, R >0 , lim R 0 + ( e 1 R ) R = lim 1 R + ( e R ) 1 R = e \displaystyle \lim_{R \to 0^{+}} (e^{\frac{1}{R}})^{R} = \lim_{\frac{1}{R} \to + \infty} (e^R)^{\frac{1}{R}} = e , and taking i R , such that R R , R > 0 iR, \text{ such that } R \in \mathbb{R}, R >0 , lim R 0 + ( e 1 i R ) i R = lim R 0 + e i R ( i k ) = 1 \displaystyle \lim_{R \to 0^{+}} (e^{\frac{1}{iR}})^{iR} = \lim_{R \to 0^{+}} e^{iR(ik)} = 1 due to k ( π , π ] k \in (\pi, \pi] and k k is the main argument of e 1 i R e^{\frac{1}{iR}} , ( Arg e 1 i R \text{ Arg }e^{\frac{1}{iR}} ), ln e 1 i R = ln e i R = ln 1 + i k \ln e^{\frac{1}{iR}} = \ln e^{\frac{-i}{R}}= \ln 1 + ik

HOW CAN WE DEDUCE THE FIRST STEP ?

Kushal Bose - 4 years, 2 months ago

Log in to reply

lim z 0 ( e z ) 1 z = lim z 0 ( 1 + z ) 1 z \displaystyle \lim_{z \to 0} (e^{z})^{\frac{1}{z}} = \lim_{z \to 0} (1 + z)^{\frac{1}{z}} . Now, you have to apply the definition in exponentiation complex, i. e,this is a set a z = { e ( z ( ln a ) ) } = { e ( z ( ln a + i arg(a) ) } a^z = \{e^{(z\cdot (\ln a))}\} = \{e^{(z\cdot (\ln |a| + i\cdot \text{arg(a)})}\} , nevertheless, by agreement a z = e ( z ( ln a + i Arg(a) ) ) = e ( z ( ln a ) ) a^z = e^{(z\cdot (\ln |a| + i\cdot \text{Arg(a)}))} = e^{(z\cdot (\ln a))} , where Arg(a) ( π , π ] , a C { 0 } \text{Arg(a)} \in (-\pi, \pi], \space \forall a \in \mathbb{C} - \{0\}

Guillermo Templado - 4 years, 2 months ago

Very good question... Sorry, I know I'm repeating my previous argument, , however, I've deleted my previous comment because I've achieved the bonus...

Guillermo Templado - 4 years, 2 months ago

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...