有關一條不是tangent的問題~對數學有熱誠的人進

事實上, "與2個圓的距離是相同的直線" 當兩圓大小不一時是不存在的 (那是一條曲線), 但我覺得你想說的是 "從該線上的任一點畫出兩邊的切線長度相等 (the tangents drawn to the circles from any point on the line are of equal length)" (這是一條直線).

因為那條線並不接觸該圓形, 所以不是切線, 而是叫 "根軸" (Radical axis). 從該線上的任一點畫出兩邊的切線長度相等, 如下圖所示:

圖片參考：http://david.sam-siu.com/radical.PNG


描述:

"The radical axis of two circles is the locusof points at which tangents drawn to both circles have the same length;in technical language, all points on the radical axis have the same power with respect to both circles.The radical axis is always a straight line and always perpendicularto the line connecting the centers of the circles, albeit closer to thecircumference of the larger circle. If the circles intersect, theradical axis is the line passing through the intersection points;similarly, if the circles are tangent,the radical axis is simply the common tangent. In general, twodisjoint, non-concentric circles can be aligned with the circles of bipolar coordinates; in that case, the radical axis is simply the y-axis;every circle on that axis that passes through the two foci intersectthe two circles orthogonally. Thus, two radii of such a circle aretangent to both circles, satisfying the definition of the radical axis."