7. Let X, A, and B be arbitrary sets such that ACX and BC X. Prove AUB CX.

1. Write out the following sets as a list of elements. If necessary you may use ... in your description. {x EZ: |x|< 10 A x < 0} {x ЄN: x ≤ 20 A x = 2y for some y = N} {n EN: 3 | n^ 1 < n < 20} {y Є Z: y² <0}

3. For each statement below, write an equivalent statement using the justification given. = y Є A or yЄ B by the definition of union = y Є A or y Є B by the definition of set complement = x = C and x & D by DeMorgan's Law =Vx (x EnFxЄEUF) by definition of subset. = (X CYUZ)A (YUZ CX) by definition of set equality

6. Let A, B, and C be arbitrary sets. Prove that A - (BNC) = (A - B) U (A – C)

2. Find the cardinality of each set. {x = Z: |x| ≤ 5} {-2, 1, 4, 7, 10,..., 52} {{7,9}, 2, {1, 2, 3, 4, 7}, {9}, {0}}

Unit 1: Logic 1. Let P be the statement "x > 5” and let Q be the statement “y +3≤ x," and let R be the statement “y Є Z.” (a) Translate the following statements to English. (b) Negate the statements symbolically (c) Write the negated statements in English. The negations should not include any implications. • (QV¬R) AP • (P⇒¬Q) VR • (PVQ)¬R 2. Let R, S, and T be arbitrary statements. Write out truth tables for the following statements. Determine whether they are a tautology or a contradiction or neither, with justification. ⚫ (RAS) V (¬R ⇒ S) (R¬S) V (RAS) • (TA (SV¬R)) ^ [T⇒ (R^¬S)]

10. Suppose the statement -R (SV-T) is false, and that S is true. What are the truth values of R and T? Justify your answer.

5. Rewrite the statements below as an implication (that is, in "if... then..." structure). n is an even integer, or n = 2k - 1 for some k Є Z. x²> 0 or x = 0. 6. Rewrite each statement below as a disjunction (an or statement). If I work in the summer, then I can take a vacation. • If x2 y.

4. Negate the following sentences. Then (where appropriate) indicate whether the orig- inal statement is true, or the negation is true. ⚫ If I take linear algebra, then I will do my homework or go to class. • (x > 2 or x < −2) ⇒ |x| ≥ 2 • P⇒ (QVR) ⇒(¬PV QV R) Vn EN Em E Q (nm = 1) • Ex E N Vy & Z (x. y = 1)