Author Topic: 2020S-TT1 Q1  (Read 352 times)

Milan Miladinovic

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2020S-TT1 Q1
« on: October 14, 2020, 03:42:15 PM »
I'm having trouble understanding where the $-1+i$ term comes from in the following line:
$\dfrac{e^{3z} - e^{-3z}}{e^{3z} + e^{-3z}} = 1 + 2i \implies e^{6z} = -1 + i$.

I've tried the following:
$$\begin{align*}
\dfrac{e^{3z} - e^{-3z}}{e^{3z} + e^{-3z}} &= 1 + 2i\\
\dfrac{e^{6z} - 1}{e^{6z} + 1} &= 1 + 2i\\
e^{6z} - 1 &= (1 + 2i)(e^{6z} + 1)\\
e^{6z} &= (1 + 2i)(e^{6z} + 1) + 1
\end{align*}$$

How do we get from $(1 + 2i)(e^{6z} + 1) + 1$ to $-1 + i$? Have I done something wrong somewhere in my calculation?

Maria-Clara Eberlein

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Re: 2020S-TT1 Q1
« Reply #1 on: October 14, 2020, 03:52:26 PM »
This is how I got the answer, hope this helps!

Milan Miladinovic

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Re: 2020S-TT1 Q1
« Reply #2 on: October 14, 2020, 04:11:40 PM »
Awesome, that makes sense! I was overthinking it