| 单词 | principal normal | 
| 释义 | > as lemmasprincipal normal   principal normal  n. Geometry the normal drawn to a given point on a curve and located in the plane containing the direction of curvature at that point. ΚΠ a1832    Encycl. Metrop. 		(1845)	 II. 153  				This normal, the direction of which is the limit of the direction of the line of junction, has been designated by the name of the principal normal. 1902    Amer. Jrnl. Math. 24 36  				The tangent to the involute, the principal normal to the evolute and the tangent to the spherical indicatrix of the evolutes, are parallel lines. 1999    Proc. Royal Soc. A. 455 3164  				Directional derivatives in the tangential, principal normal and binormal directions. < as lemmas  | 
	
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