1) Suppose, the expression is g(x) = x^2 - 9x + 9
2) Here a = 1, b = -9; adding and subtractin (b^2)/4a = 81/4,
g(x) = (x^2) - 9x + (81/4) - (45/4) = (x - 9/2)² - (45/4)
That is y = (x - 9/2)² - (45/4) [This is the Vertex form of Parabola equation, with its axis parallel to y-axis]
By assigning some values for x you can get corresponding values for y
Thus we get many points (x,y); plotting them on graph and joining, you will get a smooth curve, parabloa.
The vertex of the parabola is the minimum point here, which is when x - 9/2 = 0; that is x = 9/2. So vertex is (9/2, -45/4)