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What is the equation of the director circle of x² + y² − 2x − 4y − 4 = 0?
A(x − 1)² + (y − 2)² = 9
B(x − 1)² + (y − 2)² = 18
C(x + 1)² + (y + 2)² = 18
D(x − 1)² + (y − 2)² = 36
Answer & Solution
Correct answer: B. (x − 1)² + (y − 2)² = 18
The centre is (1, 2) and r² = 1 + 4 + 4 = 9, so the director circle keeps the centre with radius squared 2 × 9 = 18.
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