作业帮a,b,c,d为三维列向量A=[a,2c,3d]B=[b,5c,d].且|A|=-12,|B|=15,求|A-B|
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![a,b,c,d为三维列向量A=[a,2c,3d]B=[b,5c,d].且|A|=-12,|B|=15,求|A-B|](/uploads/image/z/12355619-59-9.jpg?t=a%2Cb%2Cc%2Cd%E4%B8%BA%E4%B8%89%E7%BB%B4%E5%88%97%E5%90%91%E9%87%8FA%3D%5Ba%2C2c%2C3d%5DB%3D%5Bb%2C5c%2Cd%5D.%E4%B8%94%7CA%7C%3D-12%2C%7CB%7C%3D15%2C%E6%B1%82%7CA-B%7C)
a,b,c,d为三维列向量A=[a,2c,3d]B=[b,5c,d].且|A|=-12,|B|=15,求|A-B|
a,b,c,d为三维列向量A=[a,2c,3d]B=[b,5c,d].且|A|=-12,|B|=15,求|A-B|
a,b,c,d为三维列向量A=[a,2c,3d]B=[b,5c,d].且|A|=-12,|B|=15,求|A-B|
|A-B|
= |a-b, 3c, 2d|
= |a, 3c, 2d| - |b, 3c, 2d|
= 6|a,c,d| - 6|b,c,d|
= |a,2c,3d| - 6/5|b,5c,d|
= |A|-6/5|B|
= -12 -(6/5)*15
= -30.