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8.1 Conics
Conic sections are cross sections of a cone.
The three basic conics are:
1) Parabola 2) Ellipse 3) Hyperbola
The general conic equation is a quadratic in two variables:
Ax2 + Bxy + Cy2 + Dx + Ey + F=0
x
y
x
y
x
y
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Parabola
A parabola is the set of all points in a plane equidistant from a line the directrix and a point – the focus.
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Parabola
Standard Eqn: x2=4py or y2=4px
Opens: Up or down Right or leftFocus (0,p) (p,0)Directrix y=p x=pAxis yaxis xaxisFocal length p pFocal width |4p| |4p|
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Ex. 1
Find the focus, directrix and focal width of the parabola y = 4x2
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Ex. 2
Find an equation in standard form for the parabola whose directrix is the line x=3 and whose focus is the point (3,0).
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Parabola vertex (h,k)
Standard Eqn: (xh)2=4p(yk) or (yk)2=4p(xh)
Opens: Up or down Right or leftFocus (h,k+p) (h+p,k)Directrix y=kp x=hpAxis x=h y=kFocal length p pFocal width |4p| |4p|
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Ex. 3 Find the standard form of the parabola with vertex (5,5) and focus (3,5).
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Ex. 4
Prove that the graph of y2 4x + 6y +29=0is a parabola, find its vertex, focus and directrix and sketch the parabola. Confirm this on your grapher.
Ex. 5
Find the equation of the parabola with focus (4, 6) and directrix y=1.
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Ex. 6
The reflector of a television satellite dish is a paraboloid of revolution with diameter 5ft and a depth of 2ft. How far from the vertex should the antenna be placed?