Determine If the Equation $x ^ { 2 } + y ^ { 2 } = 49$

Determine if the equation $x ^ { 2 } + y ^ { 2 } = 49$ defines y as a function of x

A) The equation represents a function because it's a circle
B) The equation represents a function because for each value of x there is always two values of y
C) Not a function because the equation gives two values of y for a given value of x
D) The equation represents a function because it passes the vertical line test
E) Not a function because the equation passes the vertical line test.