**Input:**
A complex number in polar form $x = re^{i\theta}$.

**Goal:**
Return the Cartesian representation of $x = a + bi$ as a `Complex`.

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A video explanation of this conversion can be found [here](https://www.youtube.com/watch?v=auywa7dydAk).

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> Q# function `ComplexPolarAsComplex` from `Microsoft.Quantum.Math` namespace converts a complex number of type `ComplexPolar` to a complex number of type `Complex`. For educational purposes, try to do this task by hand.
