✔ 最佳答案
(Assume E, F are the folding point on AD and BC respectively.)As AE = FC = x cm, say, so ED = BF = (10-x) cm.After folding, D coincides B, so triangle ABE is a right-angled triangle. EB^2 = AE^2 + AB^2(10 - x)^2 = x^2 + 8^2100 - 20x + x^2 = x^2 + 64Therefore, x = 1.8That is, AE = FC = 1.8 cm, ED = BF = 8.2 cmAs ABFE is a right-angled trapezium, so,EF^2 = AB^2 + (CF - AE)^2EF^2 = 8^2 + (8.2 - 1.8)^2EF^2 = 64 + 40.96 = 104.96Therefore, EF = 1.6√41 cm.
2014-01-20 19:16:51 補充:
貓 Sir, 這是你教曉我的。
2014-01-20 23:30:00 補充:
是的 AE = C'F, 因為三角形AEB與C'FB全等 (ASA)
因為 104.96 = 1.6 x 1.6 x 41
所以 √104.96 = 1.6√41
2014-01-21 08:49:19 補充:
不是 "想出", 是 "計出".
也不是 "快", "慢" 的問題.
你可以先換成整數, 再用平方數因式分解.
104.96
= 10496 / 100
= (4 x 4 x 4 x 4 x 41) / (10 x 10)