Let K be a subfield of a field L. Let f(x) and g(x) be polynomials in K[x].
(a) If f(x) is a factor of g(x) in L[x], prove that f(x) is also a factor of g(x) in K[x].
(b) If f(x) and g(x) have a common factor of positive degree in L[x], prove that they also have a common factor of positive degree in K[x].