三角形ABC中,向量AB点乘向量AC=1,向量AB点乘向量BC=-3(1)求AB边的长度(2)求sin(A-B)/sinC的值1)向量AB(向量AC-BC)=4向量AB*向量AB=4AB=22)AB*AC*cosA=1AB*BC*cosB=-3(AC*cosA)/(BC*cosB)=-1/3根据正弦定理(sinB*co
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![三角形ABC中,向量AB点乘向量AC=1,向量AB点乘向量BC=-3(1)求AB边的长度(2)求sin(A-B)/sinC的值1)向量AB(向量AC-BC)=4向量AB*向量AB=4AB=22)AB*AC*cosA=1AB*BC*cosB=-3(AC*cosA)/(BC*cosB)=-1/3根据正弦定理(sinB*co](/uploads/image/z/5337787-67-7.jpg?t=%E4%B8%89%E8%A7%92%E5%BD%A2ABC%E4%B8%AD%2C%E5%90%91%E9%87%8FAB%E7%82%B9%E4%B9%98%E5%90%91%E9%87%8FAC%3D1%2C%E5%90%91%E9%87%8FAB%E7%82%B9%E4%B9%98%E5%90%91%E9%87%8FBC%3D-3%EF%BC%881%EF%BC%89%E6%B1%82AB%E8%BE%B9%E7%9A%84%E9%95%BF%E5%BA%A6%EF%BC%882%EF%BC%89%E6%B1%82sin%EF%BC%88A-B%EF%BC%89%2FsinC%E7%9A%84%E5%80%BC1%29%E5%90%91%E9%87%8FAB%28%E5%90%91%E9%87%8FAC-BC%29%3D4%E5%90%91%E9%87%8FAB%2A%E5%90%91%E9%87%8FAB%3D4AB%3D22%29AB%2AAC%2AcosA%3D1AB%2ABC%2AcosB%3D-3%28AC%2AcosA%29%2F%28BC%2AcosB%29%3D-1%2F3%E6%A0%B9%E6%8D%AE%E6%AD%A3%E5%BC%A6%E5%AE%9A%E7%90%86%EF%BC%88sinB%2Aco)
三角形ABC中,向量AB点乘向量AC=1,向量AB点乘向量BC=-3(1)求AB边的长度(2)求sin(A-B)/sinC的值1)向量AB(向量AC-BC)=4向量AB*向量AB=4AB=22)AB*AC*cosA=1AB*BC*cosB=-3(AC*cosA)/(BC*cosB)=-1/3根据正弦定理(sinB*co
三角形ABC中,向量AB点乘向量AC=1,向量AB点乘向量BC=-3(1)求AB边的长度(2)求sin(A-B)/sinC的值
1)向量AB(向量AC-BC)=4
向量AB*向量AB=4
AB=2
2)AB*AC*cosA=1
AB*BC*cosB=-3
(AC*cosA)/(BC*cosB)=-1/3
根据正弦定理
(sinB*cosA)/(sinA*cosB)=-1/3
-3sinBcosA=sinAcosB
带入sin(A-B)/sinC=sin(A-B)/sin(A+B)=2中
【【2)AB*AC*cosA=1
AB*BC*cosB=-3】】是怎么来的?
三角形ABC中,向量AB点乘向量AC=1,向量AB点乘向量BC=-3(1)求AB边的长度(2)求sin(A-B)/sinC的值1)向量AB(向量AC-BC)=4向量AB*向量AB=4AB=22)AB*AC*cosA=1AB*BC*cosB=-3(AC*cosA)/(BC*cosB)=-1/3根据正弦定理(sinB*co
向量的点乘就等于向量模的乘机乘上两向量夹角的余弦值
答案 1)向量AB(向量AC-BC)=4
向量AB*向量AB=4
AB=2
2)AB*AC*cosA=1
AB*BC*cosB=-3
两式比一下
(AC*cosA)/(BC*cosB)=-1/3
根据正弦定理
(sinB*cosA)/(sinA*cosB)=-1/3
-3sinBcosA=sinAcosB
带入sin(A-B)/sinC=sin(A-B)/sin(A+B)=2中