Tell whether each of the following is true for all sets

Question

A, B If false, give a counterexample.

a. A-B= A-0 (with slashed O)
b. AUB (with line over AUB) = AUB (with line over A and a line over B)

Answer 1

a. true
b. false
U = {1,2,3,4,5}
A = {1,2,3}
B = {2,4,5}

A' = {4,5}
B' = {1,3}

(AUB)' = {}
A'UB' = {1,3,4,5}
However A' ∩ B' = {}