'''Purpose:''' Usage help for the '''sqrt''' math function.
----
The call,
    [expr { sqrt($x) }]
returns the square root of $x.
----
If you're using ''sqrt'' in connection with the Pythagorean Theorem:

    [expr { sqrt( $x * $x + $y * $y ) }]

note that Tcl provides a [hypot] function, which gives a more concise
formula:

    [expr { hypot( $x, $y ) }]

The [hypot] function is also more robust in that it will get
overflow and underflow less often when dealing with very large or
very small numbers.

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