已知a,b,c是同一平面内的三个向量,其中a=(1,2).(1)若|b|=3√5,且b‖a求b的坐标.(2)若c与a的夹角θ的余弦值为-√5/10,且(a+c)⊥(a-9c),求|c|
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![已知a,b,c是同一平面内的三个向量,其中a=(1,2).(1)若|b|=3√5,且b‖a求b的坐标.(2)若c与a的夹角θ的余弦值为-√5/10,且(a+c)⊥(a-9c),求|c|](/uploads/image/z/1580873-41-3.jpg?t=%E5%B7%B2%E7%9F%A5a%2Cb%2Cc%E6%98%AF%E5%90%8C%E4%B8%80%E5%B9%B3%E9%9D%A2%E5%86%85%E7%9A%84%E4%B8%89%E4%B8%AA%E5%90%91%E9%87%8F%2C%E5%85%B6%E4%B8%ADa%3D%281%2C2%29.%281%29%E8%8B%A5%7Cb%7C%3D3%E2%88%9A5%2C%E4%B8%94b%E2%80%96a%E6%B1%82b%E7%9A%84%E5%9D%90%E6%A0%87.%EF%BC%882%EF%BC%89%E8%8B%A5c%E4%B8%8Ea%E7%9A%84%E5%A4%B9%E8%A7%92%CE%B8%E7%9A%84%E4%BD%99%E5%BC%A6%E5%80%BC%E4%B8%BA-%E2%88%9A5%2F10%2C%E4%B8%94%EF%BC%88a%2Bc%EF%BC%89%E2%8A%A5%EF%BC%88a-9c%EF%BC%89%2C%E6%B1%82%EF%BD%9Cc%EF%BD%9C)
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