Final answer:
There are no excluded values for the expression x^2 - 4 since it is a polynomial with no restrictions on the values that x can take.
Step-by-step explanation:
The student has provided the expression x^2 − 4 and is asking how many excluded value(s) there are. An excluded value is a value that cannot be used for the variable in the expression because it may cause division by zero or some other undefined operation. In this context, since the expression is x^2 - 4, there are no excluded values because this is a simple polynomial, which is defined for all real numbers. A polynomial does not have a denominator that could be zero, so it won't cause division by zero. Therefore, you can use any real number as a substitution for x.