CS 205 - Problem Set 3 - Sets and Summations
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CS 205 - Problem Set 3 - Sets and Summations
Due 9pm Thursday, March 2nd 2023
Problem 1
1. Prove that there are no solutions in integers x and y to the equation 2x2 + 5y2 = 14. (5pts)
2. Prove or disprove that you can use dominos to tile a 5 × 5 checkerboard with three corners removed. (5pts)
Problem 2
Find the truth set of each of the following predicates where the domain is the set of integers.
• P(x) : x3 ≥ 1 (2pts)
• Q(x) : x2 = 2 (2pts)
• R(x) : x < x2 (2pts)
• T(x) : x2 − 2x + 1 ≥ 0 (2pts)
Problem 3
Show that if A,B are sets, then the symmetric difference A ⊕ B, containing the elements in either A or B but not in both A and B .
• A ⊕ B=B ⊕ A. (5pts)
• (A ⊕ B) ⊕ B = A. (5pts)
Problem 4
Give an example of a function from N to N that is
• one-to-one but not onto; (3pts)
• onto but not one-to-one; (3pts)
• both onto and one-to-one (but different from the identity function) (3pts)
• neither one-to-one nor onto. (3pts)
Problem 5
Show that if x is a real number and n is an integers, then
• x ≤ n if and only if ⌈x⌉ ≤ n; (5pts)
• n ≤ x if and only if n ≤「x⌋ . (5pts)
2023-03-06