(本题满分10分)如图,已知AB是⊙O的直径,点C在⊙O上,过点C的直线与AB的延长线交于点P,AC=PC,∠COB=
(本题满分10分)如图,已知AB是⊙O的直径,点C在⊙O上,过点C的直线与AB的延长线交于点P,AC=PC,∠COB=2∠PCB.(1)求证:PC是⊙O的切线;(2)求证...
(本题满分10分)如图,已知AB是⊙O的直径,点C在⊙O上,过点C的直线与AB的延长线交于点P,AC=PC,∠COB=2∠PCB. (1)求证:PC是⊙O的切线;(2)求证:BC= AB;(3)点M是弧AB 的中点,CM交AB于点N,若AB=4,求MN·MC的值.
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(1)PC是⊙O的 切线,证明略。 (2)BC= ![](https://iknow-pic.cdn.bcebos.com/730e0cf3d7ca7bcba00a679dbd096b63f624a80b?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) AB,证明略。 (3)MC·MN=BM 2 =8 |
(本题满分10分) 解:(1)∵OA=OC,∴∠A=∠ACO ∵∠COB=2∠ ![](https://iknow-pic.cdn.bcebos.com/09fa513d269759eea621c079b1fb43166d22df0b?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) A ,∠COB=2∠PCB ∴∠A=∠ACO=∠PCB ……………………………… ![](https://iknow-pic.cdn.bcebos.com/08f790529822720eabbf424878cb0a46f21fab0b?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) ……………………1分 ∵AB是⊙O的直径 ∴∠ACO+∠OCB=90° …………………………………………………2分 ∴∠PCB+∠OCB=90°,即OC⊥CP …………………………………………3分 ∵OC是⊙O的半径 ∴PC是⊙O的切线 …………………………………………………4分 ![](https://iknow-pic.cdn.bcebos.com/9922720e0cf3d7cad2879fc4f11fbe096b63a90b?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) (2)∵PC="AC " ∴∠A=∠P ∴∠A=∠ACO=∠PCB=∠P ∵∠COB=∠A+∠ACO,∠CBO=∠P+∠PCB ∴∠CBO=∠COB ……………………………………………5分 ∴BC=OC ∴BC= ![](https://iknow-pic.cdn.bcebos.com/730e0cf3d7ca7bcba00a679dbd096b63f624a80b?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) AB ………………………………………………………6分 (3)连接MA,MB ∵点M是弧AB的中点 ∴弧AM=弧BM ∴∠ACM=∠BCM ………7分 ∵∠ACM=∠ABM ∴∠BCM=∠ABM ∵∠BMC=∠BMN ∴△MBN∽△MCB ∴ ∴BM 2 =MC·MN ……………………8分 ∵AB是⊙O的直径 ![](https://iknow-pic.cdn.bcebos.com/f7246b600c33874459b48fce520fd9f9d72aa00b?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) ,弧AM=弧BM ∴∠AMB=90°,AM=BM ∵AB="4 " ∴BM= ![](https://iknow-pic.cdn.bcebos.com/eaf81a4c510fd9f96166f5db262dd42a2834a40b?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) ………………………………………………………9分 ∴MC·MN=BM 2 ="8 " ……………………………………………………10分 |
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