已知a,b,c,d四个实数，算24点。 令f1(x) = a, f2(x) = b, f3(x) = c, f4(x) = d 所以 f1'(x) = f2'(x) = f3'(x) = f4'(x) = 0 0! = 1 所以[(a)'] ! + [(b)'] ! + [(c)'] ! + [(d)'] ! = 4, 4! = 24