Voorbeelden van het gebruik van Projectivity in het Engels en hun vertalingen in het Nederlands
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Then X.l is a projectivity from i onto i.
Let P be the Pappus point of this projectivity.
This projectivity φ induces the conic mentioned in the problem.
Construct thet Pappus point of the projectivity.
Φ(x), where φ is a projectivity from the pencil of lines L onto a pencil of lines M.
Prove that the mapping X→ TX is a projectivity.
If the projectivity is a perspectivity,
First construct the Pappus point P of the projectivity.
This projectivity induces on every line i(not through I or M) a projectivity XL.
but then the projectivity is trivial.
O40 Let φ be a projectivity from l onto m,
According to the second proposition of§10, θ is a projectivity.
A conic, because φ is a projectivity and induces a projectivity from A onto B.
According to the previous proposition, f is a projectivity from i onto m.
The restriction of π to l is a projectivity from the pencil of points l to the pencil of lines L.
are collinear on the Pappus line of the projectivity.
Proposition: A bijection ψ: l→ m is a projectivity if and only if ψ preserves cross ratio.
perspectivities a projectivity.
Note: Each projectivity φ: L→ M is the restriction to L of a projective transformation of P2.
Theorem of Steiner: Let J be a conic and φ a projectivity from J onto J.
Proposition: Each projectivity φ: l→ m is induced by a regular linear transformation of ℜ3.
The intersection points we have to construct are the fixed points of the projectivity induced on l.
Prove that φ induces a projectivity from the pencil of lines L onto the pencil of lines L', with L' φL.
so we have the projectivity θ: X→ π(X).l.
This projectivity induces on every line l(not through L or M) a projectivity θ: X→ φXL.
Proof: We saw in the last section but this one that any projectivity preserves cross ratio.
Likewise: a projectivity from a pencil of lines L onto itself with three invariant lines is identitity.
Study the picture above and show we can take a projectivity that is the product of three perspectivities.
Definition: A projectivity from a conic J onto itself is a bijection from J onto J that preserves cross ratio.
O84 Investigate which degenerations occur if in the definition of a conic of points L M, or if the projectivity is a perspectivity.