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.