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''of a planar curve <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m065/m065380/m0653801.png" />''
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''of a planar curve $F(x,y)=0$''
  
A singular point at which the partial derivatives of order up to and including <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m065/m065380/m0653802.png" /> vanish, but where at least one partial derivative of order <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m065/m065380/m0653803.png" /> does not vanish. For example, if <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m065/m065380/m0653804.png" />, <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m065/m065380/m0653805.png" />, <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m065/m065380/m0653806.png" /> does not vanish, the multiple point <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m065/m065380/m0653807.png" /> is called a [[Double point|double point]]; if the first and second partial derivatives vanish at <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m065/m065380/m0653808.png" />, but at least one third derivative does not, the multiple point is called a triple point; etc.
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A singular point at which the partial derivatives of order up to and including $n$ vanish, but where at least one partial derivative of order $n+1$ does not vanish. For example, if $F(x_0,y_0)=0$, $F_x'(x_0,y_0)=0$, $F_{yy}''(x_0,y_0)$ does not vanish, the multiple point $M(x_0,y_0)$ is called a [[double point]]; if the first and second partial derivatives vanish at $M(x_0,y_0)$, but at least one third derivative does not, the multiple point is called a triple point; etc.
  
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====References====
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<table><TR><TD valign="top">[a1]</TD> <TD valign="top"> J.L. Coolidge, "Algebraic plane curves" , Dover, reprint (1959) {{MR|0120551}} {{ZBL|0085.36403}} </TD></TR><TR><TD valign="top">[a2]</TD> <TD valign="top"> D. Hilbert, S.E. Cohn-Vossen, "Geometry and the imagination" , Chelsea (1952) pp. 173 (Translated from German) {{MR|0046650}} {{ZBL|0047.38806}} </TD></TR><TR><TD valign="top">[a3]</TD> <TD valign="top"> P.A. Griffiths, J.E. Harris, "Principles of algebraic geometry" , Wiley (Interscience) (1978) {{MR|0507725}} {{ZBL|0408.14001}} </TD></TR><TR><TD valign="top">[a4]</TD> <TD valign="top"> W. Fulton, "Algebraic curves" , Benjamin (1969) pp. 66 {{MR|0313252}} {{MR|0260752}} {{ZBL|0194.21901}} {{ZBL|0181.23901}} </TD></TR></table>
  
 
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[[Category:Algebraic geometry]]
====Comments====
 
 
 
 
 
====References====
 
<table><TR><TD valign="top">[a1]</TD> <TD valign="top">  J.L. Coolidge,  "Algebraic plane curves" , Dover, reprint  (1959)</TD></TR><TR><TD valign="top">[a2]</TD> <TD valign="top">  D. Hilbert,  S.E. Cohn-Vossen,  "Geometry and the imagination" , Chelsea  (1952)  pp. 173  (Translated from German)</TD></TR><TR><TD valign="top">[a3]</TD> <TD valign="top">  P.A. Griffiths,  J.E. Harris,  "Principles of algebraic geometry" , Wiley (Interscience)  (1978)</TD></TR><TR><TD valign="top">[a4]</TD> <TD valign="top">  W. Fulton,  "Algebraic curves" , Benjamin  (1969)  pp. 66</TD></TR></table>
 

Latest revision as of 16:52, 8 April 2023

of a planar curve $F(x,y)=0$

A singular point at which the partial derivatives of order up to and including $n$ vanish, but where at least one partial derivative of order $n+1$ does not vanish. For example, if $F(x_0,y_0)=0$, $F_x'(x_0,y_0)=0$, $F_{yy}''(x_0,y_0)$ does not vanish, the multiple point $M(x_0,y_0)$ is called a double point; if the first and second partial derivatives vanish at $M(x_0,y_0)$, but at least one third derivative does not, the multiple point is called a triple point; etc.

References

[a1] J.L. Coolidge, "Algebraic plane curves" , Dover, reprint (1959) MR0120551 Zbl 0085.36403
[a2] D. Hilbert, S.E. Cohn-Vossen, "Geometry and the imagination" , Chelsea (1952) pp. 173 (Translated from German) MR0046650 Zbl 0047.38806
[a3] P.A. Griffiths, J.E. Harris, "Principles of algebraic geometry" , Wiley (Interscience) (1978) MR0507725 Zbl 0408.14001
[a4] W. Fulton, "Algebraic curves" , Benjamin (1969) pp. 66 MR0313252 MR0260752 Zbl 0194.21901 Zbl 0181.23901
How to Cite This Entry:
Multiple point. Encyclopedia of Mathematics. URL: http://encyclopediaofmath.org/index.php?title=Multiple_point&oldid=15154
This article was adapted from an original article by A.B. Ivanov (originator), which appeared in Encyclopedia of Mathematics - ISBN 1402006098. See original article