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Secant plane
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This article is about the cross-section of the sphere. For other uses, see Secant (disambiguation).
A secant plane is a plane containing a nontrivial section of a sphere or an ellipsoid, or such a plane that a sphere is projected onto. Secant planes are similar to tangent planes, which contact the sphere's surface at a point, while secant planes contact the surface along curves.
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The two-dimensional representations of secant planes are secant lines, the lines that join two distinct points on a curve.