Does x^2+y^2=9 represent y as a function of x?​

No, x²+y²= 9 does not represent y as a function of x.

For x= 0,

y²= 9

=>y= ±3,

i.e y has two values +3 and -3

Since single value of x , there are two values of y

For an equation or relation to be function every element in domain( every value of x) there should one distinct value or image in co-domain (one value of y)

lo ; )