1. Conic Sections Dr. Shildneck Fall, 2015

2. Parabolas CONIC SECTIONS

3. Parabolas DEFINITION focus directrix A parabola is the locus of points such that every point is equidistant from a fixed point (called the focus) and a fixed line (called the directrix). FOCUSDIRECTRIX

4. Parabolas Standard Equations (x-h) 2 = 4p(y-k) (y-k) 2 = 4p(x-h) h = x-coordinate of the vertex k = y-coordinate of the vertex p = distance from the vertex to the focus (sign indicates direction) -p = distance from the vertex to the directrix |4p| = distance across the parabola through the focus If the x-term is squared, the parabola opens vertically If the y-term is squared, the parabola opens horizontally

5. Quick Graphs 1.Determine the orientation 2.Find and Plot Vertex 3.Find p and plot the focus 4.Graph the directrix 5.Find 4p and find each point (2p) from the focus. Quick Graphs 1.Determine the orientation 2.Find and Plot Vertex 3.Find p and plot the focus 4.Graph the directrix 5.Find 4p and find each point (2p) from the focus. Example 8(x+7) = (y-2) 2 Example 8(x+7) = (y-2) 2 Vertex ( - 7, 2) Find p 4p = 8 p = 2 Focus is 2 to the right Directrix is 2 left Direction Y is squared (left/right) 4p is positive (up/right)

6. Writing Equations 1.Know the standard form of the equation 2.Often it helps if you sketch the curve described 3.Find any critical values needed for the equation 4.Plug those into the equation

7. Example 1 Write the equation of the parabola Example 1 Write the equation of the parabola Vertex: (-2, 4) Opens: down So, x is squared P: down 4; p= - 4 (x-h) 2 =4p(y-k) h pk ANSWER (x +2) 2 = – 16(y– 4 ) ANSWER (x +2) 2 = – 16(y– 4 )

8. Examples Write the equation of the parabola with the following characteristics. 2.Vertex (4, -2) and focus (4, 7) 3.Vertex (5, -4) and directrix x = 8 4.Focus (-2, 4) and directrix y = 1 5.Vertex (3,1) opens vertically passing through (5, 9)

9. Assignment Alternate Text (on website) P. 667 Vocabulary #4-7 Exercises #37-42, 43, 45, 51, 53, 56, 59, 65, 73, 77, 81, 91, 93