Final answer:
The domain of the function f(x) = -3x + 12 is all real numbers, which is represented in interval notation as (-∞, ∞).
Step-by-step explanation:
The domain of a function is the set of all possible input values (x values) for which the function is defined. In the case of the linear function f(x) = -3x + 12, the function is defined for all real numbers, because there is no value of 'x' that would make the function undefined. So, the domain of this function is all real numbers, which in interval notation is expressed as (-∞, ∞).