Question

Which of the following is not a function?

(a) {(1,2), (2,4), (3,6)}

(b) {(-1,1), (-2,4), (2,4)}

(c) {(1,2), (1,4), (2,5), (3,8)}

(d) {(1,1), (2,2), (3,3)}

I got this question in final exam.

Origin of the question is Functions topic in portion Relations and Functions of Mathematics – Class 11

Answer 1

Correct answer is (c) {(1,2), (1,4), (2,5), (3,8)}

The explanation: A relation from a set A to a set B is said to be a function if every element of set A has one and one image in set B.

In {(1,2), (1,4), (2,5), (3,8)}, since element 1 has two images 2 and 4 which is not possible in a function so, it is not a function. Rest all have one and only one image so they can be called a function.