zero. Two such pairs are equivalent if they differ by an overall nonzero factor ?:
:

Line extended by a point at infinity

The projective line may be identified with the line K extended by a point at infinity. More precisely,the line K may be identified with the subset of P¹(K) given by
: This subset covers all points in P¹(K) except one, which is called the point at infinity:
: This allows

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