The curve y2=4ax represents a parabola with vertex at the origin.
a. (i) State the standard equation of a parabola whose axis is the x-axis and whose vertex is the origin. Also mention its vertex and axis.
b. (ii) If a point P(x1,y1) lies on this parabola, derive an expression for the parameter a in terms of x1 and y1.
c. (iii) Explain why a point with x1<0 cannot satisfy the equation y2=4ax for any real a.