What is the range of the function #x^2+y^2=36#?
That relation is not a function.
The relation is in the standard form of a circle.
Its graph is a circle of radius 6 about the origin.
Its domain is [-6, 6], and its range is also [-6, 6].
To find this algebraically, solve for y.
The range is largest in absolute value when x = 0, and we have
That is, at -6 and 6.