A treatise on solid geometry
Percival Frost
Paperback
(RareBooksClub.com, May 10, 2012)
This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1863 Excerpt: ...generating line. 299. To shew that the equation of the tangent plane to a developable surface contains only one parameter. Since the general equations of a straight line involve four arbitrary constants, we must, in order to the generation of any ruled surface, have three relations connecting these constants, so that we may eliminate the four constants and obtain the equation of a surface the locus of all the straight lines. In developable surfaces, the generating straight lines are such that any two consecutive ones intersect, and the plane containing them is ultimately a tangent plane to the surface. The equation of this plane will then involve the four parameters, and by means of the three relations we may eliminate three, so that the general equation of the tangent plane to a developable surface will involve only one parameter, and we may write it in the form z = ax + f(a)y + yr(a), a being the parameter, and p (a), (a) functions of that parameter, given in any particular case. In skew surfaces, the equation of the tangent plane at any point will involve the parameter of the generating straight line passing through the point, but not containing the consecutive straight line, will involve some other parameter which fixes the tangent plane among all the planes containing that straight line. We may also arrive at the conclusion that the equation of the tangent plane to a developable surface can only involve one parameter, from the consideration that if it involved two, we should by varying them infinitesimally, obtain the equations of three planes, which would ultimately intersect in a definite point, instead of in one straight line, so that the plane could in general have only one point of contact with the surface which it touched; and the surface would t...