如图, Rt△ABC中,∠ABC=90°,以AB为直径的⊙O交AC于点D,E为BC边的中点,连接DE.(1)求证:DE与⊙O
如图,Rt△ABC中,∠ABC=90°,以AB为直径的⊙O交AC于点D,E为BC边的中点,连接DE.(1)求证:DE与⊙O相切.(2)若tanC=,DE=2,求AD的长....
如图, Rt△ABC中,∠ABC=90°,以AB为直径的⊙O交AC于点D,E为BC边的中点,连接DE.(1)求证:DE与⊙O 相切.(2)若tanC= ,DE=2,求AD的长.
展开
(1)证明见解析;(2) ![](https://iknow-pic.cdn.bcebos.com/00e93901213fb80e79602d6535d12f2eb83894ca?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) . |
试题分析:(1)连接OD,BD,求出∠ADB=∠BDC=90°,推出DE=BE=CE,推出∠EDB=∠EBD,∠OBD=∠ODB,推出∠EDO=∠EBO=90°即可. (2)由∠BDC=90°,E为BC边的中点可得BC=4,在Rt△ABC中,由tanC= ![](https://iknow-pic.cdn.bcebos.com/30adcbef76094b365524575fa0cc7cd98c109dca?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) 可得AB=2 ![](https://iknow-pic.cdn.bcebos.com/503d269759ee3d6ded94cb7940166d224f4ade36?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) ,在Rt△ABC中,由勾股定理可得AC=6,由△ABD∽△ACB可求得AD= ![](https://iknow-pic.cdn.bcebos.com/00e93901213fb80e79602d6535d12f2eb83894ca?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) . 试题解析:(1)如图,连接BD、OD, ∵AB为⊙O的直径,∴∠ADB=∠BDC=90°. ∵E为BC边的中点,∴DE=EC.∴∠1=∠C. ∵OA=OD,∴∠2=∠A. ∵∠ABC=90°,∴∠A+∠C =90°.∴∠1+∠2 =90°. ∴∠ODE =90°.∴OD⊥DE于点D. ∵以AB为直径的⊙O交AC于点D,∴D是半径的外端. ∴DE与⊙O 相切. (2)∵∠BDC=90°,E为BC边的中点,∴ ![](https://iknow-pic.cdn.bcebos.com/63d0f703918fa0ecbb9528bf259759ee3d6ddb36?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) . ∵DE=2,∴BC=4. 在Rt△ABC中,tanC= ![](https://iknow-pic.cdn.bcebos.com/f603918fa0ec08fae5525f155aee3d6d55fbda36?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) ,∴AB=BC· ![](https://iknow-pic.cdn.bcebos.com/a1ec08fa513d2697ef8144ef56fbb2fb4316d836?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) =2 ![](https://iknow-pic.cdn.bcebos.com/503d269759ee3d6ded94cb7940166d224f4ade36?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) . 在Rt△ABC中,AC= ![](https://iknow-pic.cdn.bcebos.com/adaf2edda3cc7cd9709b786b3a01213fb90e91ca?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) , 又∵△ABD∽△ACB,∴ ![](https://iknow-pic.cdn.bcebos.com/2fdda3cc7cd98d10ff624083223fb80e7aec90ca?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) ,即 ![](https://iknow-pic.cdn.bcebos.com/a2cc7cd98d1001e9c68a58bdbb0e7bec55e797ca?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) . ∴AD= ![](https://iknow-pic.cdn.bcebos.com/00e93901213fb80e79602d6535d12f2eb83894ca?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) . |
收起
为你推荐: