Question

Write the set {x : x is a natural number and x^2-9=0} in roster form.

(a) {3}

(b) {-3}

(c) {3,-3}

(d) {9,3}

I had been asked this question during an interview.

I'd like to ask this question from Sets and their Representations in portion Sets of Mathematics – Class 11

Answer 1

The correct answer is (a) {3}

The best explanation: Since x is given as natural number so x can be positive only.                                      x^2-9=0 => (x-3)(x+3)=0  =>  x=3,-3.

Here, -3 is not a natural number so, the set {x : x is a natural number and x^2-9=0} can be written as {3}.