Chord of contactMediumQuestion 320007
Question
From external point (x₁, y₁), the chord of contact to x² + y² = r² has equation:
- Axx₁ + yy₁ = r²Correct
- Bx²+y²=r²
- Cy−y₁ = m(x−x₁)
- Dx/x₁+y/y₁=1
Correct answer
xx₁ + yy₁ = r²
Explanation
The chord of contact (the chord joining the two points of tangency) from external point (x₁,y₁) to circle x²+y²=r² has equation xx₁+yy₁=r² — same form as the tangent equation at a point on the circle.