Given a = {X / x = 3K-1, K ∈ Z}, fill in the blanks with ∈ or &; sign. (1) 5 A; (2) 7 A; (3) - 10 A

Given a = {X / x = 3K-1, K ∈ Z}, fill in the blanks with ∈ or &; sign. (1) 5 A; (2) 7 A; (3) - 10 A

It's still you. You should understand
(1) As long as we get an integer k such that x = 5, then 5 is the element of set A. obviously, when k = 2, it holds, so 5 ∈ a
(2) There is no integer k such that x = 7, so 7 does not belong to set a
(3) There is an integer k = - 3 such that x = - 10, so - 10 belongs to the set a

Fill in the blanks with appropriate symbols: A, B ∈ R, then (a + b) ^ 2______ 4ab

(a-b)^2≥0
a^2-2ab+b^2≥0
Add 4AB on both sides
a^2+2ab+b^2≥4ab
So (a + b) ^ 2 ≥ 4AB

5 = 2 fill in the symbol
5 5 5 5=3 5 5 5 5=4 5 5 5 5=1

5÷ 5 +5 ÷5=2