已知向量m=(1,0),n=(1/2,-√3/2),且a=m+2n,b=2m-3n,求a与b的夹角答案=120°
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![已知向量m=(1,0),n=(1/2,-√3/2),且a=m+2n,b=2m-3n,求a与b的夹角答案=120°](/uploads/image/z/3174215-23-5.jpg?t=%E5%B7%B2%E7%9F%A5%E5%90%91%E9%87%8Fm%3D%281%2C0%29%2Cn%3D%281%2F2%2C-%E2%88%9A3%2F2%EF%BC%89%2C%E4%B8%94a%3Dm%2B2n%2Cb%3D2m-3n%2C%E6%B1%82a%E4%B8%8Eb%E7%9A%84%E5%A4%B9%E8%A7%92%E7%AD%94%E6%A1%88%3D120%C2%B0)
已知向量m=(1,0),n=(1/2,-√3/2),且a=m+2n,b=2m-3n,求a与b的夹角答案=120°
已知向量m=(1,0),n=(1/2,-√3/2),且a=m+2n,b=2m-3n,求a与b的夹角
答案=120°
已知向量m=(1,0),n=(1/2,-√3/2),且a=m+2n,b=2m-3n,求a与b的夹角答案=120°
a=m+2n=(2,-√3)
b=2m-3n=(1/2,3√3/2)
cos=a*b/|a||b|=(1-9/2)/(√7)^2=-1/2
a与b的夹角=120°