Let A(x1,y1,z1) and B(x2,y2,z2) be the endpoints of a diameter of a sphere.
a. (i) Explain why the midpoint O of AB is the centre of the sphere.
b. (ii) Show that the length of the radius is 21(x2−x1)2+(y2−y1)2+(z2−z1)2.
c. (iii) Hence derive the general equation of the sphere whose diameter is AB.