Hi everyone,

This time I have a little bit confuse when I try to solve this question that I think it is obviously shown:

(a) Show that there is a line through any pair of points in the plane. [Hint: Every line has equation ax + by + c = 0, where a, b, c are not all zero].

(b) Generalize and show that there is a plane ax + by + cz + d = 0 through any three points in space.

(Source: Question 6, Section 1.3, Chapter 1, Linear Algebra with Applications 5th Edition, W. Keith Nicholson)

At first I think it is so easy but after that I can not think how can I prove when it is too obviously. It made me going crazy and frustrated. Or maybe I have some problem in thinking (stupid or something ?) that I can not solve this.

Thank you so much.