✔ 最佳答案
32.
答案是: (B) 15/4
已知:BC = CD = 12 及 BF = 3
所以 FC = BC -BF = 12 - 3 = 9
在 ΔFCD中:
FD² = CD² + FC² (勾股定理)
FD² = 12² + 9²
FD² = 225
FD = 15
∠BFE + 90° + ∠DFC = 180° (直線同側鄰角和)
∠CDF + 90° + ∠DFC = 180° (直線同側鄰角和)
所以 ∠BFE = ∠CDF (公理)
而 ∠FBE = ∠DCF = 90° (正方形內角)
因此 ΔBFE =CDF (AAA)
BF/CD = EF/FD (相似Δ對應邊)
3/12 = EF/15
EF = (3/12) x 15
EF = 15/4