✔ 最佳答案
............. A
............. / . \
............/..... \
..... G. /____\ F
........ /.|........|.\
...... /...|____|...\
.... B...D......E...C
設正方形 DEFG 邊長 = x :
則 △ABC = 25 + 40 + 60 + x² = x² + 125
又 △AGF 高 = 50/x , 得 △ABC 高 = x + 50/x
BD = 80/x , EC = 120/x
故 △ABC = (1/2) (x + 50/x) (BD + DE + EC)
= (1/2) (x + 50/x) (80/x + x + 120/x)
解 x² + 125 = (1/2) (x + 50/x) (80/x + x + 120/x)
2x⁴+ 250x² = (x² + 50) (x² + 200)
2x⁴+ 250x² = x⁴+ 250x² + 10000
x⁴= 10000
x = 10∴ BC = 80/10 + 10 + 120/10 = 30