Solution
Related Formula
For a line y = mx + c and hyperbola (x²)/(a²) - (y²)/(b²) = 1: If they do not intersect, the quadratic in x formed by substituting y has D < 0.Core Logic
Given line: α x + 2y = 1 y = (1 - α x)/(2). Given hyperbola: x² - 9y² = 9.
Substitute the expression for y into the hyperbola's equation:
x² - 9((1 - α x)/(2))² = 9Step 1: Solving for Discriminant
x² - (9(1 - 2α x + α² x²))/(4) = 9Multiply by 4:
4x² - 9(1 - 2α x + α² x²) = 36 4x² - 9 + 18α x - 9α² x² - 36 = 0 (4 - 9α²)x² + 18α x - 45 = 0For the line to NOT intersect the hyperbola, the quadratic must yield non-real roots, meaning Discriminant D < 0.
D = (18α)² - 4(4 - 9α²)(-45) < 0 324α² + 180(4 - 9α²) < 0 324α² + 720 - 1620α² < 0 -1296α² + 720 < 0 1296α² > 720 α² > (720)/(1296) = (5)/(9)Step 2: Finding Alpha Interval
α² - (5)/(9) > 0 α in (-∞, - √(5)3) ( √(5)3, ∞)Since √(5) ≈ 2.236, we have √(5)3 ≈ 0.745. So α must be strictly greater than 0.745 (or less than -0.745).
Checking the given options: (1) 0.6 (No) (2) 0.8 (Yes, 0.8 > 0.745) (3) 0.5 (No) (4) 0.7 (No)
Pattern Recognition
Geometrically, for a line not to meet a hyperbola, its slope must lie within a specific range determined by the asymptotes (m = ± b/a), and its c² must satisfy c² < a²m² - b². Direct substitution to enforce D < 0 is purely mechanical and robust.
Chapter Mix
Class 11 Maths: Conic Sections