Find the minimum and maximum values of the function f(x) = -12x² + 24 on the interval [1,7] by comparing values at the critical points and endpoints.
a) Minimum at x = 1, maximum at x = 7
b) Minimum at x = 7, maximum at x = 1
c) Minimum at x = 1, maximum at x = 7 and vice versa
d) There is no minimum or maximum value in the given interval