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The linear maps (or linear functions) of vector spaces, viewed as geometric maps, map lines to lines; that is, they map collinear point sets to collinear point sets and so, are collineations. In projective geometry these linear mappings are called homographies and are just one type of collineation.
Formally, let V be a vector space over a field K and W a vector space over a field L. Consider the projective spaces PG(V) and PG(W), consisting of the vector lines of V and W. Call D(V) and D(W) the set of subspaces of V and W respectively. A collineation from PG(V) to PG(W) is a map α : D(V) → D(W), such that: α is a bijection.
Let X be an affine space over a field k, and V be its associated vector space. An affine transformation is a bijection f from X onto itself that is an affine map; this means that a linear map g from V to V is well defined by the equation () = (); here, as usual, the subtraction of two points denotes the free vector from the second point to the first one, and "well-defined" means that ...
For example, for any two distinct points, there is a unique line containing them, and any two distinct lines intersect at most at one point. [ 1 ] : 300 In two dimensions (i.e., the Euclidean plane ), two lines that do not intersect are called parallel .
Similarly, three generic points in the plane are not collinear; if three points are collinear (even stronger, if two coincide), this is a degenerate case. This notion is important in mathematics and its applications, because degenerate cases may require an exceptional treatment; for example, when stating general theorems or giving precise ...
The study of functions of a complex variable is known as complex analysis and has enormous practical use in applied mathematics as well as in other branches of mathematics. Often, the most natural proofs for statements in real analysis or even number theory employ techniques from complex analysis (see prime number theorem for an example).
The dual V ∗ of a finite-dimensional (right) vector space V over a skewfield K can be regarded as a (right) vector space of the same dimension over the opposite skewfield K o. There is thus an inclusion-reversing bijection between the projective spaces PG(n, K) and PG(n, K o). If K and K o are isomorphic then there exists a duality on PG(n, K).
In mathematics it is a common convention to express the normal as a unit vector, but the above argument holds for a normal vector of any non-zero length. Conversely, it is easily shown that if a , b , c , and d are constants and a , b , and c are not all zero, then the graph of the equation a x + b y + c z + d = 0 , {\displaystyle ax+by+cz+d=0 ...