The square root of a complex number can have two values

See e.g. this example: https://www.wolframalpha.com/input/?i=square+root+of+-8+-8i
So Sqrt should be prepared to return up to 2 values. Or at least the documentation should state that only one value is returned - and which one.

---
#### Document Details

⚠ *Do not edit this section. It is required for docs.microsoft.com ➟ GitHub issue linking.*

* ID: 2494ea85-3e79-0784-30ee-ee23961a3f8f
* Version Independent ID: 63d22dfb-3124-4c78-b82a-291a4c58a2d4
* Content: [Complex.Sqrt(Complex) Method (System.Numerics)](https://docs.microsoft.com/en-us/dotnet/api/system.numerics.complex.sqrt?f1url=https%3A%2F%2Fmsdn.microsoft.com%2Fquery%2Fdev15.query%3FappId%3DDev15IDEF1%26l%3DEN-US%26k%3Dk(System.Numerics.Complex.Sqrt);k(TargetFrameworkMoniker-.NETFramework,Version%3Dv4.7.1);k(DevLang-csharp)%26rd%3Dtrue&view=netframework-4.7.2)
* Content Source: [xml/System.Numerics/Complex.xml](https://github.com/dotnet/dotnet-api-docs/blob/master/xml/System.Numerics/Complex.xml)
* Product: **dotnet-api**
* GitHub Login: @dotnet-bot
* Microsoft Alias: **dotnetcontent**