Asystem of equations has infinitely many solutions. if 2y – 4x = 6 is one of the equations, which could be the other equation?
y = 2x 6
y = 4x 6
–y = –2x – 3
–y = –4x 6

A system of equations has infinitely many solutions when the two lines representing the equations coincide. i.e. the two equations are the same.
2y - 4x = 6
2y = 4x + 6
2y = 2(2x + 3)
y = 2x + 3
-y = -(2x + 3)
-y = -2x - 3
Hence the other equation is -y = -2x - 3