Which one of the following is not a function?
select one:
a. y = x2 – 4x + 2 incorrect
b. x = y2 – 4y + 2
c. y = |x – 2|
d. y= /x-2 incorrect

Function here describes y(x), x is the input, y is the output.

A single input or x-value can only yield 1 output or y-value otherwise it is NOT a function.

For example if x = 4 but y could be 2 or -2, Then this is not a y(x) function.
THis can happen when y has an exponent.
x = y^2  > 4 = 2^2 = (-2)^2

Therefore answer is b) x = y^2-4y+2