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Question
Find the angle between the vectors `hati-hatj and hatj-hatk`
Solution
`Let veca = hati − hatj; vecb = hatj− hatk`
`veca . vecb=(hat i-hat j).(hat j-hat k)=` 1 x 0 +(-1) x 1 + 0 x (-1)=-1
`|veca|=sqrt(1^2+(-1)^2+0^2)=sqrt2`
`|vecb|=sqrt(0^2+1^2+(_1)^2)=sqrt2`
We know that `veca.vecb=|veca||vecb|cos theta`
Thus,`costheta=(veca.vecb)/(|veca||vecb|)=-1/(sqrt2 xx sqrt2)=-1/2`
`=> costheta=cos 120^@`
`=> theta= 120^@`
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