Question: what is the formula of x-axis?
Answer: The equation of x-axis is y = 0, since, x-axis is a parallel to itself at a distance 0 from it. Let P (x,y) be any point on the x-axis. Then clearly, for all position of P we shall the same ordinate 0 or, y = 0. Therefore, the equation of x-axis is y = 0.