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5. For a function f : A - B and subsets E and F of B, prove f-'(E - F) = f-'(E) -f-'(F). 6. Let f : R - R be the function defined by f(x) = x2 + ax + b, where a, be R. Determine whether f is injective and/or surjective. 7. For n E N, let A = {a1, a2, a3, . .. , an} be a fixed set and let F be the set of all functions f : A - {0, 1}. What is | F), the cardinality of F? Now, for P(A), the power set of A, consider the function 9 : F - P(A), defined as g(f) = {a E A : f(a) = 1}. Is g injective? Is g surjective