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Math for Non-Geeks/ Exercises: Exponential and Logarithm functions
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Range of the exponential function
Show that
You are supposed to show that holds for all .
We have already shown that holds for all . Let be an arbitrary complex number with , .
How can we express using and ?
Using the exponential functional equation, we get
As , holds if and only if . A good trick to show that a number is not equal to is to show that its absolute value (or the square of its absolute value) is unequal to .
What is ?
Using the computation rules for complex numbers, we get
Hence, we have and the claim follows.
We have already shown that holds for all . Furthermore, for all , holds that . Hence, for all follows that .
Let be an arbitrary complex number. Then there exist such that . It follows that .
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