如图,AB是⊙O的直径,C、P是 上两点,AB=13,AC=5,(1)如图(1),若点P是 的中点,求PA的长;(2
如图,AB是⊙O的直径,C、P是上两点,AB=13,AC=5,(1)如图(1),若点P是的中点,求PA的长;(2)如图(2),若点P是的中点,求PA得长....
如图,AB是⊙O的直径,C、P是 上两点,AB=13,AC=5,(1)如图(1),若点P是 的中点,求PA的长;(2)如图(2),若点P是 的中点,求PA得长 .
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(1) ![](https://iknow-pic.cdn.bcebos.com/00e93901213fb80e84ca286535d12f2eb938946d?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/cf1b9d16fdfaaf51e2f9c80d8f5494eef01f7a6d?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) . |
试题分析:(1)根据圆周角的定理,∠APB=90°,p是弧AB的中点,所以三角形APB是等腰三角形,利用勾股定理即可求得. (2)根据垂径定理得出OP垂直平分BC,得出OP∥AC,从而得出△ACB∽△0NP,根据对应边成比例求得ON、AN的长,利用勾股定理求得NP的长,进而求得PA. 试题解析::(1)如答图(1),连接PB, ∵AB是⊙O的直径且P是 ![](https://iknow-pic.cdn.bcebos.com/203fb80e7bec54e737f653acba389b504fc26a6d?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) 的中点,∴∠PAB=∠PBA=45°,∠APB=90°. 又∵在等腰三角形△ABC中有AB=13, ∴ ![](https://iknow-pic.cdn.bcebos.com/7aec54e736d12f2eba1fe7d24cc2d5628535686d?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) . (2)如答图(2),连接BC,与OP相交于M点,作PH⊥AB于点H, ∵P点为 ![](https://iknow-pic.cdn.bcebos.com/18d8bc3eb13533fab2ceda9cabd3fd1f41345b03?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) C的中点,∴OP⊥BC,∠OMB=90°, 又∵AB为直径,∴∠ACB=90°.∴∠ACB=∠OMB. ∴OP∥AC.∴∠CAB=∠POB. 又∵∠ACB=∠OHP=90°,∴△ACB∽△0HP.∴ ![](https://iknow-pic.cdn.bcebos.com/32fa828ba61ea8d3ce5a3db6940a304e251f5803?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) . 又∵ ![](https://iknow-pic.cdn.bcebos.com/9a504fc2d5628535edfa9b9393ef76c6a7ef636d?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) ,∴ ![](https://iknow-pic.cdn.bcebos.com/a9d3fd1f4134970a060b599d96cad1c8a7865d03?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) ,解得 ![](https://iknow-pic.cdn.bcebos.com/e4dde71190ef76c6abc8b2999e16fdfaaf51676d?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) . ∴AH=OA+OH=9. ∵在Rt△OPH中,有 ![](https://iknow-pic.cdn.bcebos.com/960a304e251f95cae88ddb04ca177f3e67095203?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) 。 ∴在RT△AHP中 有 ![](https://iknow-pic.cdn.bcebos.com/241f95cad1c8a786f25203bc6409c93d70cf5003?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) . ∴PA= ![](https://iknow-pic.cdn.bcebos.com/cf1b9d16fdfaaf51e2f9c80d8f5494eef01f7a6d?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) . |
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