Which of the following expressions represents a function?

Question

A:9
B:{(4, 2), (4, –2), (9, 3), (9, –3)}
C:x = 4
D:2x + y = 5

Answer 1

An equation is a function if for every input value 'x' there is one and only one output value f(x) 

 

9 is just a number, not a function

 

{(4,2),(4,-2),(9,3),(9,-3)} is not a function because the input value x=4 has two different output values...2, and -2.  The same for x=9 which has output values of 3, and -3

 

x=4 is not a function because this vertical line has infinite output values for the single input value of x=4 because y can be any real number  from -infinity to infinity

 

2x+y=5 graphs as a line with a slope of -2.  For every input value of x you will have only one corresponding value of y.  This is a function.

 

Your answer is D) 2x+y=5