已知线段OA⊥OB,C为OB上中点,D为AO上一点,连AC、BD交于P点. (1)如图1,当OA=OB且D为AO中点时,求
已知线段OA⊥OB,C为OB上中点,D为AO上一点,连AC、BD交于P点.(1)如图1,当OA=OB且D为AO中点时,求的值;(2)如图2,当OA=OB,=时,求△BPC...
已知线段OA⊥OB,C为OB上中点,D为AO上一点,连AC、BD交于P点. (1)如图1,当OA=OB且D为AO中点时,求 的值;(2)如图2,当OA=OB, = 时,求△BPC与△ACO的面积之比.
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解:(1)过C作CE∥OA交BD于E………………………………(1分) 由△BCE∽△BOD得CE= ![](https://iknow-pic.cdn.bcebos.com/0824ab18972bd407ec89e34f78899e510fb30931?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) OD= ![](https://iknow-pic.cdn.bcebos.com/0824ab18972bd407ec89e34f78899e510fb30931?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) AD ………………………………(1分) 再由△ECP∽△DAP得 ![](https://iknow-pic.cdn.bcebos.com/d31b0ef41bd5ad6e13b7545882cb39dbb6fd3c31?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) ………………………………(1分) (2)过C作CE∥OA交BD于E,过P作PF⊥OB交OB于F 设AD=x,AO=OB=4x,则OD=3x ……………………………………………(1分) 由△BCE∽△BOD得CE= ![](https://iknow-pic.cdn.bcebos.com/0824ab18972bd407ec89e34f78899e510fb30931?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) OD= ![](https://iknow-pic.cdn.bcebos.com/aa18972bd40735fa3cbe7e0b9d510fb30f240831?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) x, 再由△ECP∽△DAP得 ![](https://iknow-pic.cdn.bcebos.com/34fae6cd7b899e51d2c00aa641a7d933c8950d31?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) ; 由勾股定理可知BD=5x,DE= ![](https://iknow-pic.cdn.bcebos.com/7a899e510fb30f249dd4dcb1cb95d143ad4b0331?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) x,则 ![](https://iknow-pic.cdn.bcebos.com/060828381f30e924abc6ac834f086e061d95f725?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) , 可得PD=AD=x,……………………………………………………………………(2分) 则PF= ![](https://iknow-pic.cdn.bcebos.com/9f510fb30f2442a73940cd17d243ad4bd1130231?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) ,S △BPC = ![](https://iknow-pic.cdn.bcebos.com/0eb30f2442a7d93329e6d4c1ae4bd11373f00131?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) ,而S △ACO = ![](https://iknow-pic.cdn.bcebos.com/38dbb6fd5266d016dc57ae9a942bd40735fa3531?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) ,得 ![](https://iknow-pic.cdn.bcebos.com/4d086e061d950a7b1b577e7609d162d9f2d3c925?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) …………………………(2分) (1)首先过C作CE∥OA交BD于E,可得△BCE∽△BOD,根据相似三角形的对应边成比例可得CE= ![](https://iknow-pic.cdn.bcebos.com/0824ab18972bd407ec89e34f78899e510fb30931?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) OD= ![](https://iknow-pic.cdn.bcebos.com/0824ab18972bd407ec89e34f78899e510fb30931?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) AD ,再由△ECP∽△DAP,即可求得答案; (2)首先过C作CE∥OA交BD于E,过P作PF⊥OB交OB于F,然后设设AD=x,AO=OB=4x,则OD=3x,由△BCE∽△BOD得CE=CE= ![](https://iknow-pic.cdn.bcebos.com/0824ab18972bd407ec89e34f78899e510fb30931?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) OD= ![](https://iknow-pic.cdn.bcebos.com/aa18972bd40735fa3cbe7e0b9d510fb30f240831?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) x,再由△ECP∽△DAP得 又由勾股定理可知BD=5x,DE= ![](https://iknow-pic.cdn.bcebos.com/7a899e510fb30f249dd4dcb1cb95d143ad4b0331?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) x,则可求得PF=1 ![](https://iknow-pic.cdn.bcebos.com/9f510fb30f2442a73940cd17d243ad4bd1130231?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) ,S △BPC = ![](https://iknow-pic.cdn.bcebos.com/0eb30f2442a7d93329e6d4c1ae4bd11373f00131?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) ,而S △ACO =4x 2 ,继而求得答案. |
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