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The vertices of a hyperbola are at [tex]$(-5,-2)$[/tex] and [tex]$(-5,12)$[/tex], and the point [tex]$(-5,30)$[/tex] is one of its foci. What is the equation of this hyperbola?

A. [tex]$\frac{(y-5)^2}{24^2}-\frac{(x+5)^2}{7^2}=1$[/tex]

B. [tex]$\frac{(x+5)^2}{24^2}-\frac{(y-5)^2}{7^2}=1$[/tex]

C. [tex]$\frac{(x+5)^2}{7^2}-\frac{(y-5)^2}{24^2}=1$[/tex]

D. [tex]$\frac{(y-5)^2}{7^2}-\frac{(x+5)^2}{24^2}=1$[/tex]


Sagot :

To determine the equation of the hyperbola, let's follow these steps:

1. Identify the center: The center \((h, k)\) of the hyperbola is the midpoint of the vertices \((-5,-2)\) and \((-5,12)\).
[tex]\[ h = -5 \][/tex]
[tex]\[ k = \frac{-2 + 12}{2} = \frac{10}{2} = 5 \][/tex]

2. Calculate the semi-major axis \(a\): The distance between the vertices is the length of the major axis, so:

The length of the major axis is:
[tex]\[ 12 - (-2) = 14 \][/tex]
The semi-major axis \(a\) is half of this distance:
[tex]\[ a = \frac{14}{2} = 7 \][/tex]

3. Calculate the distance \(c\) from the center to the foci: The distance from the center \((-5, 5)\) to one of the foci \((-5, 30)\) is:
[tex]\[ c = 30 - 5 = 25 \][/tex]

4. Calculate the semi-minor axis \(b\): Using the relationship among \(a\), \(b\), and \(c\):
[tex]\[ c^2 = a^2 + b^2 \][/tex]
Substitute the known values:
[tex]\[ 25^2 = 7^2 + b^2 \][/tex]
[tex]\[ 625 = 49 + b^2 \][/tex]
Solving for \(b^2\), we get:
[tex]\[ b^2 = 625 - 49 = 576 \][/tex]
Thus,
[tex]\[ b = \sqrt{576} = 24 \][/tex]

5. Determine the equation: Based on the center, vertices, and foci's configuration, this hyperbola opens vertically, i.e., it has a shape \(\frac{(y - k)^2}{a^2} - \frac{(x - h)^2}{b^2} = 1\).

With the values we have calculated:
[tex]\[ (h, k) = (-5, 5) \][/tex]
The semi-major axis \(a\) is 7, and \(a^2 = 49\).
The semi-minor axis \(b\) is 24, and \(b^2 = 576\).

Therefore, the equation of this hyperbola is:
[tex]\[ \frac{(y - 5)^2}{49} - \frac{(x + 5)^2}{576} = 1 \][/tex]

Now, comparing this with the given options:
A. \(\frac{(y-5)^2}{24^2}-\frac{(x+5)^2}{7^2}=1\)
B. \(\frac{(x+5)^2}{24^2}-\frac{(y-5)^2}{7^2}=1\)
C. \(\frac{(x+5)^2}{7^2}-\frac{(y-5)^2}{24^2}=1\)
D. \(\frac{(y-5)^2}{7^2}-\frac{(x+5)^2}{24^2}=1\)

The correct answer corresponds to:

A. \(\frac{(y-5)^2}{24^2}-\frac{(x+5)^2}{7^2}=1\)

Therefore, the correct answer is:
[tex]\[ \boxed{\text{A}} \][/tex]