Analytic geometry and principles of algebra (1913)
Ziwet, Alexander, 1853-1928, Hopkins, Louis Allen, joint author, Hedrick, E. R. (Earle Raymond), 1876-1943 · New York, The Macmillan Company · leaf 184
x, y) of the parabola from the focus istherefore V(.v — a)- -\- y^, and the dis-tance QP of P from the directrix isa -f 0.. Hence the equation is which reduces at once to(3) 2/2 = 4 ax. This then is the cartesian equation of the parabola, referredto vertex and axis. i.e. when the vertex is taken as… … Fig. m 172 PLANE ANALYTIC GEOMETRY [IX, § 176 176. Negative Values of a. In the last article the constanta was again regarded as positive ; but (compare § 173) the equa-tion (3) still represents a parabola when a is a negative number,the only difference being that in this case the parabola turns…
Geometry, Analytic
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