Algebra II Section 8-2 Parabolas (the dreaded lesson)
Conic Sections
Find a point equidistant from (2, 3) and the line y = -1 Distance from (x, y) to (2, 3)=Distance from (x, y) to (x, -1) This is a parabola!
Properties of Parabolas All incoming parallel rays are reflected to the same point (focus). This is true for light, sound, radio, …
Vertex = (h, k) Focus Line segment through the focus Parallel to the directrix Name : Latus Rectum. a ky Directrix 4 1
Sideways? See chart on page 422 Mythbusters Illusion
Parabola A Parabola B Focus of A Focus of B
Find the Focus, Vertex, Directrix, Axis of Sym., Length of the L.R. y = -2x 2 – 20x + 9 Put in Vertex Form y = -2(x + 5) Focus = (-5, ) Vertex = (-5, 59) Directrix y = Length of L.R. = 0.5 Axis of Sym. x = -5
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