15) Which equation does not represent a function?

A) y = 2x + 3

B) x = 4y + 7

C) 6x - 5y = 8

D) y2 = - 5x - 8

The answer is D as it can be rewritten as - ((y^2) / 5) - (8/5) = x. Solving for the x-intercepts you get - ((y^2) / 5) - (8/5) = 0 as you want to find the y values when x is zero. Solving for y you get: (y^2) / 5) + (8/5) = 0 = > (y^2) / 5) = - (8/5) = > y^2=-8 = > y = plus or minus sqrt (-8). The first problem is that you have 2 x intercepts which already makes it not a function and second sqrt (-8) is an imaginary number making the solution not a real number.