Given quadrilateral ABCD, we trisect AB,CD,BC, DA by the points P_1, P_2, Q_1, Q_2, R_1 , R_2 , S_1 , S_2 . Let N,M,L,K be the intersection points of Q_1 P_1 and S_2 R_2, Q_2 P_2 and S_2 R_2, Q_2 P_2 and S_1 R_1, Q_1 P_1 and S_1 R_1.Prove that KLMN/ABCD = 1/9.
我知道這題應該用共邊定理做……但我想不出做法。
先謝。