Question 1028199
y is not a function of x.


start with x + y^2 = 4


subtract x from both sides of the equation to get y^2 = 4-x


take the square root of both sides of the equation to get y = plus or minus sqrt(4-x).


you are getting 2 values of y for every value of x.


that means that y is not a function of x.


in order for it to be a function, you must get one and only one value of y for each and every value of x.