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 | | For example, section 523 of the Chelsea edition has a table of 23 kinds of cubic surfaces, classified according to their singularities and giving the class and number of lines on the surface in each case. |
 | | (Salmon uses the terminology "reciprocal surface" but is not referring to this transformation; instead, he means what we would call the dual surface.) If one of the coefficients a,b,c,d vanishes, say a, then the cubic is reducible and has a line of singularlties at least. |
 | | Assuming I have guessed correctly, the class of this surface should be 4 and it should have exactly 9 lines on it, according to the table. |
| www.math.niu.edu /~rusin/known-math/99/cubic_surf (1005 words) |
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