A line l in P" is a one-dimensional projective variety of the form { = 5. V,(f1,..., fr), where each f; is (homogeneous) of degree 1. a) Show that there are two disjoint lines in P" if and only if n > 3. b) Show that if lị and l2 are two disjoint lines in P³ and a € P³ a point not belonging to l1 U l2, then there exists a unique line containing a and intersecting (1 and l2.

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5.
A line l in P" is a one-dimensional projective variety of the form l =
V,(f1,..., fr), where each f; is (homogeneous) of degree 1.
a) Show that there are two disjoint lines in F" if and only if n > 3.
b) Show that if ly and l2 are two disjoint lines in P3 and a e P a point
not belonging to lı U l2, then there exists a unique line containing a and
intersecting l1 and l2.
c) What further conditions need to be imposed for b) to be true in the affine
setting, with l1 and l2 two ordinary lines and a E A³ a point not belonging
to either?
Transcribed Image Text:5. A line l in P" is a one-dimensional projective variety of the form l = V,(f1,..., fr), where each f; is (homogeneous) of degree 1. a) Show that there are two disjoint lines in F" if and only if n > 3. b) Show that if ly and l2 are two disjoint lines in P3 and a e P a point not belonging to lı U l2, then there exists a unique line containing a and intersecting l1 and l2. c) What further conditions need to be imposed for b) to be true in the affine setting, with l1 and l2 two ordinary lines and a E A³ a point not belonging to either?
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