Consider the surface given by x2 + y2 - z2 = a. Graph this in GeoGebra then answer questions 7 through 10 using your online graph. Note: You will need to change the value for the slider given for a to a minimum of -20 a maximum of 20 with an increment of 1. To do so, follow the instructions found in this video. 7. What quadratic surface do you obtain when a > 0? 8. Describe what occurs as the slider moves from a = 20 to a = 0 9. Explain what occurs when a = 0. Does this make sense? Why or why not? 10. Describe what occurs when a