Question

which one is not a function?

1+y^2=x^2
6x=y^3
(y+2)^2-9x=x
7x=y^2

Answer 1

have you done the "vertical line test" before?

Answer 2

yes

Answer 3

ok, well, the 1st option there, has "y" and "x" terms squared, that is \(\bf y^2\) and \(\bf x^2\)

that's pretty much a dead giveaway is an ellipse, and if you run the vertical line test on an ellipse, well, lemme give you one so you can see if it passes