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For x² + y² − 2x + 4y + k = 0 to be a real circle, which must hold?
Ak > 5
Bk < 5
Ck < −5
Dk = 5
Answer & Solution
Correct answer: B. k < 5
g = −1, f = 2, so g² + f² − c = 5 − k must be positive, giving k < 5.
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