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if 5x+9=0 is the directrix of the hyperb...

if `5x+9=0` is the directrix of the hyperbola `16x^(2)-9y^(2)=144`, then its corresponding focus is

A

`(5,0)`

B

`(-(5)/(3),0)`

C

`(-5,0)`

D

`((5)/(3),0)`

Text Solution

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The correct Answer is:
To solve the problem, we need to find the focus of the hyperbola given its equation and the directrix. Let's break it down step by step. ### Step 1: Write the equation of the hyperbola in standard form The given equation of the hyperbola is: \[ 16x^2 - 9y^2 = 144 \] To convert it to the standard form, we divide the entire equation by 144: \[ \frac{16x^2}{144} - \frac{9y^2}{144} = 1 \] This simplifies to: \[ \frac{x^2}{9} - \frac{y^2}{16} = 1 \] From this, we can identify \( a^2 = 9 \) and \( b^2 = 16 \). ### Step 2: Calculate \( a \) and \( b \) Taking the square roots, we find: \[ a = 3, \quad b = 4 \] ### Step 3: Calculate the eccentricity \( e \) The eccentricity \( e \) of a hyperbola is given by the formula: \[ e = \sqrt{1 + \frac{b^2}{a^2}} \] Substituting the values of \( a^2 \) and \( b^2 \): \[ e = \sqrt{1 + \frac{16}{9}} = \sqrt{\frac{25}{9}} = \frac{5}{3} \] ### Step 4: Identify the directrix The equation of the directrix for a hyperbola is given by: \[ x = \frac{-a}{e} \] We are given that the directrix is \( 5x + 9 = 0 \), which can be rearranged to: \[ x = -\frac{9}{5} \] ### Step 5: Set the directrix equal to the formula Now we equate the directrix to the formula: \[ -\frac{a}{e} = -\frac{9}{5} \] Substituting \( e = \frac{5}{3} \): \[ -\frac{a}{\frac{5}{3}} = -\frac{9}{5} \] This simplifies to: \[ \frac{3a}{5} = \frac{9}{5} \] Multiplying both sides by 5: \[ 3a = 9 \] Dividing by 3: \[ a = 3 \] ### Step 6: Calculate the focus The foci of a hyperbola are located at \( (\pm ae, 0) \). Therefore, we calculate: \[ ae = 3 \cdot \frac{5}{3} = 5 \] Thus, the coordinates of the foci are: \[ (-5, 0) \quad \text{and} \quad (5, 0) \] ### Final Answer The corresponding focus of the hyperbola is: \[ \boxed{(-5, 0)} \]

To solve the problem, we need to find the focus of the hyperbola given its equation and the directrix. Let's break it down step by step. ### Step 1: Write the equation of the hyperbola in standard form The given equation of the hyperbola is: \[ 16x^2 - 9y^2 = 144 \] To convert it to the standard form, we divide the entire equation by 144: \[ ...
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