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The line y = mx + c touches x² + y² = a² when which condition holds?
Ac² = a²(1 + m²)
Bc = a(1 + m)
Cc² = a²(1 − m²)
Dc² = a² + m
Answer & Solution
Correct answer: A. c² = a²(1 + m²)
The perpendicular distance from the origin to the line equals the radius, giving c²/(1 + m²) = a².
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