JEE Main 20257 AprilEvening Shift
- Exam
- JEE Main
- Year
- 2025
- Date
- 7 April
- Shift
- Evening Shift
- Subject
- Mathematics
- Chapter
- Hyperbola
JEE Main 2025 · 7 April · Evening Shift · Mathematics · Hyperbola
Let the lengths of the transverse and conjugate axes of a hyperbola...
Let the lengths of the transverse and conjugate axes of a hyperbola in standard form be 2a and 2b, respectively, and one focus and the corresponding directrix of this hyperbola be and , respectively. If the product of the focal distances of a point on the hyperbola is , then is equal to
Correct answer
0
Step-by-step solution
Equation of hyperbola is (\frac{\mathrm{x}^2}{\mathrm{a}^2}-\frac{\mathrm{y}^2}{\mathrm{~b}^2}=1)
Directrix: (\mathrm{x}=\frac{-9}{5}) and corresponding foci
(\Rightarrow-\frac{\mathrm{a}}{\mathrm{e}}=-\frac{9}{5}) and (-\mathrm{ae}=-5)
(\Rightarrow \frac{9 e^2}{5}=5 \Rightarrow e=\sqrt{\frac{25}{9}}=\frac{5}{3} \Rightarrow a=3)
(\therefore \mathrm{b}^2=\mathrm{a}^2\left(\mathrm{e}^2-1\right)=9\left(\frac{25}{9}-1\right)=16)
Hyperbola (\frac{\mathrm{x}^2}{9}-\frac{\mathrm{y}^2}{16}=1)
((\alpha, 2 \sqrt{5})) lie on it
(\Rightarrow \frac{\alpha^2}{9}-\frac{20}{16}=1 \Rightarrow \alpha^2=\frac{36}{16} \times 9=\frac{81}{4})
Product for distance of (\left(\mathrm{x}_1 \mathrm{y}_1\right)) from the two foci
)((\alpha, 2 \sqrt{5}) \Rightarrow \mathrm{P}=\frac{25}{9} \cdot \frac{81}{4}-9=\frac{189}{4})
(4 \mathrm{P}=189)$