What will happen if you try to call Math.sqrt() with a negative number?

When calling Math.sqrt() with a negative number, the result is NaN, which stands for "Not-a-Number." This behavior occurs because, in the context of real numbers, the square root of a negative number does not yield a valid result. Instead, it is mathematically represented as a complex number, but JavaScript's Math.sqrt() function is designed to handle only real numbers, which is why it returns NaN instead of throwing an error or crashing the program.

Understanding this helps illustrate how functions in programming languages can handle mathematical operations that may not have a valid output within their defined number system. Thus, using a negative input in this case leads to a specific, defined output rather than an unexpected program failure or incorrect result.