4. Suppose X is a finite set and A, B C X. Show that if |A| + |B| > |X|+ 3, then |AN B| 2 3.

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Q4 Mathmetical reasoning. Please with full explanation and steps. I struggle with this topic very much. Explanation and typed answers will be appreciated. Thanks!
1. Let f : X →Y be a function.
(a) Prove that f(B1 N B2) = f(B1) n f(B2) for any B1, B2, E P(Y).
(b) Prove that f(A N A2) s f(A1)n f (A2) for any A1, A2 E P(X). Give an example
of a specific function f and sets A1, A, such that f(A1) n f(A2) Z f(AN Az2)
2. Let f : X →Y be a function.
(a) Prove that f is injective + f is injective + f is surjective.
(b) Prove that f is surjective + f is surjective + f is injective.
(Hint: when proving statements of the form P Q R, it is often easier to prove
P = Q = R → P than to prove P Q and Q R)
3. Prove Corollary 10.2.2 from class: for any n E Z4, if X1,. .. , Xn are finite sets which
are pairwise disjoint, then
Ux =EX:|.
i=1
i=1
n
(Recall that U X; = X1 U X, U ...UX,
{x]x € X; for some i e {1,2,..,n}} by
i=1
definition).
4. Suppose X is a finite set and A, B C X. Show that if |A| + |B| > |X| + 3, then
|AN B| > 3.
5. Prove the following theorem from class:
Theorem 1. Suppose that X and Y are nonempty finite sets with |X| < [Y| and
f : X → Y is a function. Then f is not a surjection.
6. Prove the following theorem from class:
Theorem 2. Suppose that X and Y are finite sets with |X| = |Y\. Then a function
f: X → Y is injective if and only if it is surjective.
Transcribed Image Text:1. Let f : X →Y be a function. (a) Prove that f(B1 N B2) = f(B1) n f(B2) for any B1, B2, E P(Y). (b) Prove that f(A N A2) s f(A1)n f (A2) for any A1, A2 E P(X). Give an example of a specific function f and sets A1, A, such that f(A1) n f(A2) Z f(AN Az2) 2. Let f : X →Y be a function. (a) Prove that f is injective + f is injective + f is surjective. (b) Prove that f is surjective + f is surjective + f is injective. (Hint: when proving statements of the form P Q R, it is often easier to prove P = Q = R → P than to prove P Q and Q R) 3. Prove Corollary 10.2.2 from class: for any n E Z4, if X1,. .. , Xn are finite sets which are pairwise disjoint, then Ux =EX:|. i=1 i=1 n (Recall that U X; = X1 U X, U ...UX, {x]x € X; for some i e {1,2,..,n}} by i=1 definition). 4. Suppose X is a finite set and A, B C X. Show that if |A| + |B| > |X| + 3, then |AN B| > 3. 5. Prove the following theorem from class: Theorem 1. Suppose that X and Y are nonempty finite sets with |X| < [Y| and f : X → Y is a function. Then f is not a surjection. 6. Prove the following theorem from class: Theorem 2. Suppose that X and Y are finite sets with |X| = |Y\. Then a function f: X → Y is injective if and only if it is surjective.
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