抱歉,向量这一截我学的有点犯晕.麻烦各位帮下忙!1.若IaI=1,IbI=2,c=a+b,且c垂直于a,则向量a与b的夹角为( ).A.30° B.60° C.120° D.150° 2.已知平面上三点A、B、C满足IABI=3,IBCI=4,ICAI=5,则AB·BC+CA·BC+CA·AB
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![抱歉,向量这一截我学的有点犯晕.麻烦各位帮下忙!1.若IaI=1,IbI=2,c=a+b,且c垂直于a,则向量a与b的夹角为( ).A.30° B.60° C.120° D.150° 2.已知平面上三点A、B、C满足IABI=3,IBCI=4,ICAI=5,则AB·BC+CA·BC+CA·AB](/uploads/image/z/1262522-2-2.jpg?t=%E6%8A%B1%E6%AD%89%2C%E5%90%91%E9%87%8F%E8%BF%99%E4%B8%80%E6%88%AA%E6%88%91%E5%AD%A6%E7%9A%84%E6%9C%89%E7%82%B9%E7%8A%AF%E6%99%95.%E9%BA%BB%E7%83%A6%E5%90%84%E4%BD%8D%E5%B8%AE%E4%B8%8B%E5%BF%99%211.%E8%8B%A5IaI%3D1%2CIbI%3D2%2Cc%3Da%2Bb%2C%E4%B8%94c%E5%9E%82%E7%9B%B4%E4%BA%8Ea%2C%E5%88%99%E5%90%91%E9%87%8Fa%E4%B8%8Eb%E7%9A%84%E5%A4%B9%E8%A7%92%E4%B8%BA%EF%BC%88+%EF%BC%89.A.30%C2%B0+B.60%C2%B0+C.120%C2%B0+D.150%C2%B0+2.%E5%B7%B2%E7%9F%A5%E5%B9%B3%E9%9D%A2%E4%B8%8A%E4%B8%89%E7%82%B9A%E3%80%81B%E3%80%81C%E6%BB%A1%E8%B6%B3IABI%3D3%2CIBCI%3D4%2CICAI%3D5%2C%E5%88%99AB%C2%B7BC%2BCA%C2%B7BC%2BCA%C2%B7AB)
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