由题意可得
CB•CA=1×2×cos60°=1,
∴CM•CA=(CB+BM)•CA
=CB•CA+BM•CA
=1+2BA•CA
=1+2(CA-CB)•CA
=1+2CA^2-2 CB•CA
=1-8+2
=7
以上过程均省略了向量符号,请你注意一下就好.
由题意可得
CB•CA=1×2×cos60°=1,
∴CM•CA=(CB+BM)•CA
=CB•CA+BM•CA
=1+2BA•CA
=1+2(CA-CB)•CA
=1+2CA^2-2 CB•CA
=1-8+2
=7
以上过程均省略了向量符号,请你注意一下就好.