In Java (IEEE 754 math), what does the following print? System.out.println(Math.sqrt(-4D));

Introduction / Context:
Java’s Math library follows IEEE 754 floating-point rules. The square root of a negative real number is not defined in the reals, so Math.sqrt returns the special floating-point value NaN (Not-a-Number) rather than throwing an exception.

Given Data / Assumptions:

• Argument is -4D, a double literal.
• We are using Math.sqrt(double).

Concept / Approach:
For negative inputs, many Math functions are defined to return NaN. Java does not use exceptions for these domain errors in the Math class; instead, it propagates NaN, which prints as the string "NaN".

Step-by-Step Solution:

Verification / Alternative check:
Double.isNaN(Math.sqrt(-4)) returns true. To compute square roots of negative numbers as complex values, use a complex number library instead of Math.sqrt.

Why Other Options Are Wrong:

• -2: would be the real square root of +4, not -4.
• Compile Error / Runtime Exception: not thrown for this method.
• Infinity: returned by operations like division by zero for nonzero numerators, not here.

Common Pitfalls:
Expecting exceptions from Math for domain errors; in Java, NaN is the standard signal value.

Final Answer:
NaN