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Binormal

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The straight line passing through a point of a curve L perpendicular to the osculating plane to L at M_0. If \mathbf r=\mathbf r(t) is a parametrization of L, then the vector equation of the binormal at M_0 corresponding to the value t_0 of the parameter t has the form

\mathbf S(\lambda)=\mathbf r(t_0)+\lambda[\mathbf r'(t_0),\mathbf r''(t_0)].


Comments

This definition holds for space curves for which \mathbf r''(t_0) does not depend linearly on \mathbf r'(t_0), i.e. the curvature should not vanish.

For curves in a higher-dimensional Euclidean space, the binormal is generated by the second normal vector in the Frénet frame (cf. Frénet trihedron), which is perpendicular to the plane spanned by \mathbf r'(t_0) and \mathbf r''(t_0) and depends linearly on \mathbf r'(t_0),\mathbf r''(t_0),\mathbf r'''(t_0) (cf. [a1]).

References

[a1] M. Spivak, "A comprehensive introduction to differential geometry" , 2 , Publish or Perish (1970) pp. 1–5
How to Cite This Entry:
Binormal. Encyclopedia of Mathematics. URL: http://encyclopediaofmath.org/index.php?title=Binormal&oldid=49668
This article was adapted from an original article by E.V. Shikin (originator), which appeared in Encyclopedia of Mathematics - ISBN 1402006098. See original article