Question

If x and y are elements in the set of real numbers, which is not a function?

• A. $f=\left\{\right(x,y)/y=x^2+1\}$
• B. $f=\left\{\right(x,y)/y=2x^3\}$
• C. $f=\left\{\right(x,y)/y=9-x^2\}$
• D. $f=\left\{\right(x,y)/y\ge x+1\}$
• E. $f=\left\{\right(x,y)/y=x^2+|x|\}$

Answer 1

Answer: (D)

$f=\left\{\right(x,y)/y\ge x+1\}$

• Given relation between $x$ and $y$
• For this relation to be not a function , for one value of $x$ there should be more than one value of $y$
• Consider $y\ge x+1$ , here for one value of $x$ , there are so many values of $y$. So it is not a function
• Therefore the correct option is $D$