Question
Let a > 0, b > 0. Let e and l respectively be the eccentricity and length of the latus rectum of the hyperbola . Let e' and l' respectively be the eccentricity and length of the latus rectum of its conjugate hyperbola. If and , then the value of is equal to :
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Solution
Introduction to Hyperbolas and Their Conjugates
This problem requires a solid understanding of the fundamental properties of a hyperbola and its conjugate. Specifically, we need to recall the formulas for their eccentricity and the length of their latus rectum.
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Standard Hyperbola (): A standard hyperbola with its transverse axis along the x-axis has the equation:
- Eccentricity (): This value measures how "open" the hyperbola is. For a hyperbola, . The relationship between and is given by:
- Length of Latus Rectum (): The latus rectum is a chord passing through a focus and perpendicular to the transverse axis. Its length is:
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Conjugate Hyperbola (): The conjugate hyperbola to has its transverse axis along the y-axis. Its equation is: When defining its properties, the semi-transverse axis becomes and the semi-conjugate axis becomes . This effectively swaps the roles of and in the formulas for eccentricity and latus rectum compared to the standard hyperbola.
- Eccentricity (): For the conjugate hyperbola, the relationship between and is: Self-check: Notice how and have swapped positions in the fraction compared to the standard hyperbola's eccentricity formula.
- Length of Latus Rectum (): For the conjugate hyperbola, its length of latus rectum is: Self-check: Similarly, and have swapped roles in this formula.
Now, let's apply these definitions to solve the given problem step-by-