The use of a 3-significant-digit value for pi means that the answer must be rounded to 3 significant digits. If the 8-inch value for radius is really only accurate to ±1/2 inch, then the answer must be rounded to 1 significant digit: 40 in^2.
Because and are defined for all (i.e. their domain is ), so they can never be undefined. However, , which is undefined, because you can't divide by . So, the answer is