x - MathnMind
x - MathnMind
x - MathnMind
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Your Notes<br />
Homework<br />
Example 2 Use eccentricity to write an equation<br />
Write an equation of a hyperbola with center (21, 3),<br />
vertex (3, 3), and e 5 3.<br />
Solution<br />
Use the form (x2h)2 (y2k)2<br />
} 2 } 5 1. The vertex lies<br />
a2 b2 3 2 (21) 5 4 units from the center, so a 5 4 .<br />
Because e 5 c<br />
}<br />
a 5 3, you know that c<br />
} 5 3, or c 5 12 .<br />
4<br />
So, b2 5 c22a2 5 144 2 16 5 128 .<br />
The equation is<br />
(x 1 1)2<br />
}<br />
16<br />
2 (y 2 3)2<br />
}<br />
128<br />
5 1.<br />
Example 3 Use eccentricity to write a model<br />
An asteroid orbits the sun in an elliptical path with<br />
the sun at one focus. The eccentricity of the orbit<br />
is e 5 0.229 and the length of the major axis is 9.0<br />
astronomical units (A.U). Find an equation of the<br />
orbit. (Assume that the major axis is horizontal.)<br />
Solution<br />
The equation of the orbit has the form x2 y2<br />
} 1 } 5 1. You<br />
a2 b2 know that 2a 5 9.0 , or a 5 4.5 .<br />
e 5 c<br />
}<br />
a , so 0.229 5 c<br />
} , or c ≈ 1.03. For an ellipse,<br />
4.5<br />
c2 = a22 b2 , so b = Ï }<br />
a2 2c2 5 Ï }}<br />
(4.5) 2 2 (1.03) 2 ≈ 4.4<br />
So, an equation for the asteroid’s orbit is<br />
x2 y2 x2 y2<br />
} 1 } 5 1 or } 1 } 5 1, where x and y are<br />
(4.5) 2 (4.4) 2 20 19<br />
measured in A.U.<br />
Checkpoint Complete the following exercise.<br />
3. For another asteroid, the eccentricity of the orbit is<br />
e = 0.459 and the length of the major axis<br />
(horizontal) is 14.8 A.U. Find an equation of the<br />
asteroid’s orbit. x2 y2<br />
} 1 } 5 1<br />
55 43<br />
258 9.7 Focus On Graphing Algebra 2 Notetaking Guide Copyright © Holt McDougal. All rights reserved.