Two circlesHardQuestion 320008
Question
Two circles are orthogonal if:
- A2g₁g₂ + 2f₁f₂ = c₁ + c₂Correct
- BTheir centres coincide
- CThey are concentric
- Dr₁ = r₂
Correct answer
2g₁g₂ + 2f₁f₂ = c₁ + c₂
Explanation
Two circles are orthogonal (intersect at right angles) when 2g₁g₂ + 2f₁f₂ = c₁ + c₂. This ensures the tangent from one centre to the other circle passes through the intersection point at 90°.