Question

help.
Let A = {n ∈ Z : 2 ≤ |n| < 4}, B = {x ∈ Q : 2 < x ≤ 4}, C = {x ∈ R : x^2-(2+√2)x+2√2 = 0} and D = {x ∈ Q: x^2 - (2+√2)x + 2√2=0}

Answer 1

can someone help me explaining and finding:
1) describe the set element of A by listing its elements.
2) five an example of three elements that belong to B but do not belong to A.
3) describe the set C by listening its elements.
4) describe the set D in another manner.
5) determine the cardinality of each of the sets A, C and D.

Answer 2

here are my answers (not sure about them)
1) {2, 3}
2) {4}
3) ..
4) D = {x ∈ Q : C}

Answer 3

Your 1 is incorrect. It is missing -2, -3

Answer 4

Your 2 is missing two other elements. Consider 399/100 and 398/100

Answer 5

Your 3) is just quadratic formula.

Answer 6

why you said 399/100 and 398/100 in #2?

Answer 7

they are rational numbers

Answer 8

but they aren't integers, so they aren't in A

Answer 9

so for, 3 is correct that it is {-2.21, 1.62} ? this is the answers i got after applying the quadratic formula.