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Published online by Cambridge University Press: 20 January 2009
1. The following condition may be new; it does not appear in any of the books:—
The condition that the straight line

should be a normal to the general conic,

referred to rectangular axes, is

where Σ is written for

and Δ, A, B, C, F, G, H have their usual meanings.
* Salmon's Conics—Fifth Edition—Art. 374.