Let A = [2, 3, 5, 7]. Examine whether the statements given below are true or false.
(i) ∃ x ∈ A such that x + 3 > 9.
(ii) ∃ x ∈ A such that x is even.
(iii) ∃ x ∈ A such that x + 2 = 6.
(iv) ∀ x ∈ A, x is prime.
(v) ∀ x ∈ A, x + 2 < 10.
(vi) ∀ x ∈ A, x + 4 ≥ 11
A = [2, 3, 5, 7] (given in the question).
The given statement is: ∃ x ∈ A such that x + 3 > 9.
So, we need to see whether there exists ‘x’ which belongs to ‘A’, such that x + 3 > 9.
When x = 7 ∈ A,
x + 3 = 7 + 3 = 10 > 9
So, ∃ x ∈ A and x + 3 > 9.
So, the given statement is TRUE.
(ii) A = [2, 3, 5, 7] (given in the question).
The given statement is ∃ x ∈ A such that x is even.
So, we need to see whether there exists ‘x’ which belongs to ‘A’, such that x is even.
In the set A = [2, 3, 5, 7]
x = 2, is an even number and 2 ∈ A.
∴ ∃ x ∈ A such that x is even.
So, the given statement is TRUE.
(iii) A = [2, 3, 5, 7] (given in the question).
The given statement is: ∃ x ∈ A such that x + 2 = 6.
So, we need to see whether there exists ‘x’ which belongs to ‘A’, such that x + 2 = 6.
x = 2 → x + 2 = 4 ≠ 6
x = 3 → x + 2 = 5 ≠ 6
x = 5 → x + 2 = 7 ≠ 6
x = 7 → x + 2 = 9 ≠ 6
So, the given statement is FALSE.
(iv) A = [2, 3, 5, 7] (given in the question).
The given statement is: ∀ x ∈ A, x is prime.
So, we need to see whether for all ‘x’ which belongs to ‘A’, such that x is a prime number.
All ‘x’ which belongs to A = [2, 3, 5, 7] is a prime number.
∴∀ x ∈ A, x is prime.
So, the given statement is TRUE.
(v) A = [2, 3, 5, 7] (given in the question).
The given statement is: ∀ x ∈ A, x + 2 < 10.
So, we need to see whether for all ‘x’ which belongs to ‘A’, such that x + 2 < 10.
A = [2, 3, 5, 7]
x = 2 → x + 2 = 4 < 10
x = 3 → x + 2 = 5 < 10
x = 5 → x + 2 = 7 < 10
x = 7 → x + 2 = 9 < 10
∀ x ∈ A, x + 2 < 10, is a TRUE statement.
(vi) A = [2, 3, 5, 7] (given in the question).
The given statement is: ∀ x ∈ A, x + 4 ≥ 11.
So, we need to see whether for all ‘x’ which belongs to ‘A’, such that x + 4 ≥ 11.
A = [2, 3, 5, 7]
x = 2 → x + 4 = 6 ≥ 11
x = 3 → x + 4 = 7 ≥ 11
x = 5 → x + 4 = 9 ≥ 11
x = 7 → x + 4 = 11 ≥ 11
Only for x = 7, x + 4 = 11 ≥ 11.
∀ x ∈ A, x + 4 ≥ 11, is a FALSE statement.