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ExamsJEE AdvancedMaths

The line ax + by = 2 (with a, b nonzero) is tangent to the circle x² + y² - 2x = 3 and is also normal to the circle x² + y² - 4y = 6. Find the values of a and b respectively.

  1. 1, -1
  2. 1, 2
  3. -4/3, 1
  4. 2, 1

Correct answer: 2, 1

Solution

The line is normal to x²+y²-4y=6 (centre (0,2)), so it passes through (0,2): 2b = 2 -> b = 1; tangency to x²+y²-2x=3 (centre (1,0), radius 2) gives distance |a-2|/sqrt(a²+1) = 2, which yields a = 2 (with b = 1).

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