Question 699368

Function or Not a Function
To be a function, for each x you must have only one y value
..
x+y=9
This is a straight line so it is a function 
and 
x^2+y^2=1
This is an equation of a circle where an x can have two different y-values, therefore not a function
and 
x=y^2
This is a parabola that opens right, so like the circle an x can have two different y-values, therefore not a function