-any point on (z-1), whose symmetry point about the x axis is A'(x, y, z).

Yi Zhi: x=x 1, y 1=(x 1)/2, z 1= 1.

-

(x 1)/2，y？

+

z？ =y 1？

+

z 1？ →2(y？

+

z？ )=x？

-

2x

+

2

So the equation of this surface of revolution is 2(y?

+

z？ )=x？

-

2x

+

2。