✔ 最佳答案
Let A' be the projection of A on the line passes through PQ
and the area of ΔAPQ = (PQ)(AA')/2
in order to keep the area unchanged, AA' should be a constant, thus the locus of A are two line that parallel to PQ
here are the solution:
圖片參考:
http://imgcld.yimg.com/8/n/HA00108663/o/701206300004513873411940.jpg