... dis invertible, thenT ([(x, y)]) = [(ax + by, cx + dy)]28 Topics In Algebra Elementary Algebraic Geometry David MarkerSpring 2003Contents1 Algebraically Closed Fields 22 Affine Lines and ... = b = 0. In this case we just have the line Z = 0. Asthis line contains no points of U, we think of it as the line at in nity.Proposition 3.10 If p1, p2∈ P2(k) are distinct points, there ... distinct points in A2(k), there isa unique line containing both points.Proof We are looking for f = aX + bY + c such thatax1+ by1+ c = 0ax2+ by2+ c = 0.15This is a system of linear...