过山风GSF
幼苗
共回答了24个问题采纳率:91.7% 举报
(1)猜想:
![](https://img.yulucn.com/upload/a/6e/a6e94d7ef1a350d1b8a682fe1393c68d_thumb.jpg)
.
证明:如图,连结 OC 、 OD .
∵
![](https://img.yulucn.com/upload/e/cd/ecd7fa9b983a34667383cb0f36ac51b0_thumb.jpg)
, G 是 CD 的中点,
∴由等腰三角形的性质,有
![](https://img.yulucn.com/upload/a/6e/a6e94d7ef1a350d1b8a682fe1393c68d_thumb.jpg)
.
(2)证明:∵ AB 是⊙ O 的直径,∴∠ ACB =90°.
![](https://img.yulucn.com/upload/2/2b/22bd4bfa9764eeccb71aef8da25c0223_thumb.jpg)
而∠ CAE =∠ CBF (同弧所对的圆周角相等).
在Rt△ ACE 和Rt△ BCF 中,
∵∠ ACE =∠ BCF =90°, AC = BC ,∠ CAE =∠ CBF ,
∴Rt△ ACE ≌Rt△ BCF (ASA)
∴
![](https://img.yulucn.com/upload/2/98/298c89d51f097d96786f0fed005ed4f2_thumb.jpg)
.
(3)如图,过点 O 作 BD 的垂线,垂足为 H .则 H 为 BD 的中点.
∴ OH =
![](https://img.yulucn.com/upload/f/0f/f0fe99690baf4cf34675b0434a3e1f94_thumb.jpg)
AD ,即 AD =2 OH .
又∠ CAD =∠ BAD
![](https://img.yulucn.com/upload/8/e5/8e5836f6dd2ce4e4c78c2f52ad03e8eb_thumb.jpg)
CD = BD ,∴ OH = OG .
在Rt△ BDE 和Rt△ ADB 中,
∵∠ DBE =∠ DAC =∠ BAD ,
∴Rt△ BDE ∽Rt△ ADB
∴
![](https://img.yulucn.com/upload/e/4c/e4c8f2248b29c7628e348cc2d95904ba_thumb.jpg)
,即
∴
又
![](https://img.yulucn.com/upload/0/66/0664baf565a3cb98dcdd98285c398e56_thumb.jpg)
,∴
![](https://img.yulucn.com/upload/3/c1/3c1efbfa133bf3cd7e6a7f1077210670_thumb.jpg)
.
∴
![](https://img.yulucn.com/upload/2/ed/2ed9fdb48e0c7bddb5bcba178e32cf81_thumb.jpg)
… ①
设
![](https://img.yulucn.com/upload/6/74/67437b1206ac3d12d4ce097a4e9f8dcf_thumb.jpg)
,则
![](https://img.yulucn.com/upload/9/56/9565d32df46bf934179e1b58c6c28f76_thumb.jpg)
,AB=
![](https://img.yulucn.com/upload/6/a7/6a71ac9d8257993e857c9da1af65c23e_thumb.jpg)
.
∵ AD 是∠ BAC 的平分线,
∴
![](https://img.yulucn.com/upload/9/e2/9e272540702363d9fe6a17252c04a305_thumb.jpg)
.
在Rt△ ABD 和Rt△ AFD 中,
∵∠ ADB =∠ ADF =90°, AD = AD ,∠ FAD =∠ BAD ,
∴Rt△ ABD ≌Rt△ AFD (ASA).
∴ AF = AB =
![](https://img.yulucn.com/upload/6/a7/6a71ac9d8257993e857c9da1af65c23e_thumb.jpg)
, BD = FD .
∴ CF = AF - AC =
在Rt△ BCF 中,由勾股定理,得
![](https://img.yulucn.com/upload/0/f7/0f713ad342697acaaa088137b147988f_thumb.jpg)
…②
由①、②,得
![](https://img.yulucn.com/upload/6/57/657a7fc3fb25fb97bf3170904d49597f_thumb.jpg)
.
∴
![](https://img.yulucn.com/upload/2/7f/27fbbe10f54e1584ba4daa9c954cad2d_thumb.jpg)
.解得
![](https://img.yulucn.com/upload/1/e8/1e8128e2d689652ef993e8baaa3c8bc5_thumb.jpg)
或
![](https://img.yulucn.com/upload/2/41/241a6385333724c6dc0bbb7cc7e3e6ce_thumb.jpg)
(舍去).
∴
∴⊙ O 的半径长为
![](https://img.yulucn.com/upload/7/c8/7c874036356e01b916e1bab954fae0d3_thumb.jpg)
.
∴
1年前
4