How are a reasonable domain and range determined for a function? - Answers

By having some knowledge about the functions involved. The natural domain is the domain for which the function is defined. For example (assuming you want to work with real numbers): The square root of x is only defined for values of x greater or equal to zero. The corresponding range can also be zero or more. The sine function is defined for all real numbers. The values the function can take (the range), however, are only values between -1 and 1. A rational function (a polynomial divided by another polynomial) is defined for all values, except those where the denominator is zero. Determining the range is a bit more complicated here.