Question

Which equation is NOT a function?

y = 3x - 20
x + 2y = 8
y = x^2 - 4
x + y^2 = 16

Answer 1

x + y² = 16

Explanation:

x + y² = 16 fails the vertical line test. If you draw this horizontal parabola and then draw a vertical line through the graph, the line will intersect the parabola in 2 places. This is a sure-fire way to recognize that x + y² = 16 is not a function.