NTA Abhyas JEE Main2020MathematicsHyperbolaPractice
If a circle drawn by assuming a chord parallel to the transverse axis of hyperbola x 2 a 2 - y 2 b 2 = 1 as diameter always passes through 2,0 , then
Options
- Aa = b = 2
- Bb ≠ a
- Cb = a = 1
- Db = a = 3
Correct answer
A. a = b = 2
Step-by-step solution
Let, the end points of the diameter of circle are asec θ , b tan θ & - asec θ , b tan θ ⇒ Equation of circle is x - a sec θ x + a sec θ + y - b tan θ 2 = 0 ⇒ x 2 - a 2 sec 2 θ + y 2 + b 2 tan 2 θ - 2 b tan θ y = 0 Because 2,0 satisfies above equation, hence, 4 - a 2 1 + tan 2 θ + 0 + b 2 tan 2 θ = 0 ⇒ 4 - a 2 + b 2 - a 2 tan 2 θ = 0 Which is always true if a = 2 & b = 2