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Unformatted text preview: Horizontal Parabolas; notice that these curves do NOT represent functions. Example Find the focus and directrix of the parabola y 2 + 10 x = 0 and sketch the graph. 2 5 2 5 2 ) ( 4 10= ⇒== p x x y 2 5 2 5 : ), , ( == ⇒ x D F Horizontal parabola Example Find the focus, vertex, and directrix of the parabola ( y+1) 2 =4(x – 2) and sketch the graph. A horizontal and a vertical translation have taken place. The vertex is now (2, 1) and p = 1. The parabola opens left, so to find its focus we need to move 1 unit to the left of the vertex. Hence, F = (1, 1) The directrix is 1 unit to the right of the focus. Hence, D: x = 3. F V D Definitions A chord of a parabola is a straight line segment joining any two points on the curve. If a chord passes through the focus, it is called a focal chord. The focal width is the length of the focal chord perpendicular to the axis of symmetry. The focal width is always 4p ....
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 Fall '08
 GARDNER
 Calculus, PreCalculus, Cone, Conic Sections, Conic section, directrix

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