（1）cosP=（8+PM²-5）/2×2√2PM=√2/2PM²-4PM+3=0（PM-1)（PM-3)=0∴PM=1或者PM=3http://wenku.baidu.com/link?url=2C5AFUHtxg22TzEDFaHNISw6z8TiHu4MDyJEoJQFPFjA62XcB3N6OpSd5aA_YZ8KMEN_qY_9bdMcCBzPMP1XpeGSyR_BIAd7HYb-K9QNCAC
