Math 105–2, Summer 2023 Midterm Study Guide
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Midterm study Guide
Math 105-2, summer 2023
(1) In each part, a relation on the set R of real numbers is given. Determine if the given relation is relexive, symmetric, or transitive.
(a) x 三 g
(b) x < g
(c) x < |g|
(d) x2 + g2 = 1
(e) x2 + x = g2 + g.
(2) Let X , Y , and Z be sets and let f : X 一 Y and g : Y 一 Z be functions.
(a) If f and g are both injective prove that g 。f is injective. Does the con- verse hold?
(b) If f and g are both surjective prove that g 。f is surjective. Does the converse hold?
(c) If f and g are both bijections prove that g 。f is a bijection. Does the converse hold?
(3) Let A, B, and C be sets. prove:
(a) A U (B U C) = (A U B) U C.
(b) A U (B n C) = (A U B) n (A U C).
(c) (A n B) U (A n C) = A n (B U C).
(d) (A n B) U (B n C) U (C n A) = (A U B) n (A U C) n (B U C).
(e) (A / C) U (B / C) = (A U B) / C.
(4) Let f : X 一 Y be a function. If A and B are subsets of X is f (An B) = f (A) n f (B)?
(5) Let f : X 一 Y be a function. prove the following properties of the inverse image (aka preimage) deined in Homework 1, problem 3.
(a) A 己 f-1 (f (A)) for any subset A 己 X .
(b) f (f-1 (B)) 己 B for any subset B 己 Y.
(c) f-1 (B1 n B2 ) = f-1 (B1 ) n f-1 (B2 ) for any subsets B1 , B2 己 Y. (d) f-1 (B1 U B2 ) = f-1 (B1 ) U f-1 (B2 ) for any subsets B1 , B2 己 Y. (e) f-1 (Y / B) = X / f-1 (B) for any B 己 Y.
(6) If S is an ininite set prove that S contains an ininite subset that is countable.
(7) Let S be the collection of sequences whose terms belong to the set {0, 1}. prove that S is uncountable (mimic the proof that R is uncountable given in class).
(8) Let A be a nonempty bounded above set of integers. prove that sup(A) e A.
(9) Let p e N be a prime number. prove that^p is irrational.
(10) show that the supremum and inimum of a set are unique if they exist.
(11) Find the supremum and inimum of the following sets (if they exist):
e N}.
(b) B = {x e R| x2 - 8x + 8 < 0}.
(c) C = {x e R|(x - 2)2 > 4}.
(d) D = {x e R|(x - a)(x - b) < 0} where a, b e R are such that a < b.
(e) E = {x e R|(x - a)(x - b)(x - c) < 0} where a,b, c e R are such that a < b < c.
(12) Let A and B be two sets of positive numbers bounded above, let a = sup(A), b = sup(B). Let C be the set of all numbers of the form xg where x e A and g e B. prove that ab = sup(C).
(13) Let a, b e 政, a < b. prove that inf((a, b)) = a and sup((a, b)) = b.
(14) prove that the intersection of the open intervals (-1/n, 1/n), where n runs over the natural numbers, is equal to {0}.
(15) Recall that the kth coordinate vector in Rn , for k = 1, . . . , n, is the vector uk whose kth entry is equal to 1 and all other entries are equal to 0. prove that uk . uj = 0 if k j and IukI = 1 for all k.
(16) Let a e Rn and let R > 0. prove that if b e B(a; T) then there ex- ists a real number S 持 0 such that
B(b; S) 己 B(a; T).
2023-07-26