alleryTangent to circle x² + y² = r² at point (x₁, y₁):
Ax x₁ + y y₁ = r² (chord-of-contact form, T = 0)
Br × x
Cy = mx + c
Dx = x₁
Answer & Solution
Correct answer: A. x x₁ + y y₁ = r² (chord-of-contact form, T = 0)
Tangent to circle x² + y² = r² at point (x₁, y₁) on the circle: x x₁ + y y₁ = r².
(T = 0 rule.) Geometrically: line perpendicular to radius at the tangent point.
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