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Question
If `vecr=xhati+yhatj+zhatk` ,find `(vecrxxhati).(vecrxxhatj)+xy`
Solution
Given
`vecr=xhati+yhatj+zhatk`
`(vecrxxhati).(vecrxxhatj)+xy`
`=[(xhati+yhatj+zhatk)xxhati].[(xhati+yhatj+zhatk)xxhatj]+xy`
`=[(xhatixxhati+yhatjxxhati+zhatkxxhati)].[(xhatixxhatj+yhatjxxhatj+zhatkxxhatj)]+xy`
`=(0hati-yhatk+zhatj).(xhatk+0hatj-zhati)+xy`
`=(0z-xy+0z)+xy`
`=-xy+xy`
`=0`
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