Solution to Exercise 3.13.
God ever geometrizes.
—Plato (427–347 BCE)

Exercise 3.13. Use the propositions to justify your answer for the following.
(a) Are the points (8, 2, 1), (7, 5, 1), and (5, 11, 1) collinear?  
(a)  Use Proposition 3.1,  Hence, the points are collinear.

(b)  Are the lines [4, 2, 3], [–3, 1, 0], and [2, –7, 3] concurrent?

(a)  Use Proposition 3.2,  Hence the lines are not concurrent.