In Geometer's Sketchpad 5.03, how to draw the axis of symmetry of a parabola so that it can move left and right together with the parabola

In Geometer's Sketchpad 5.03, how to draw the axis of symmetry of a parabola so that it can move left and right together with the parabola

Choose the quadratic coefficient a and the linear coefficient b of your parabola
Calculate - B / 2a, and then draw this line. This line is x = - B / 2A