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If the vertices A,B,C of a triangle ABC ...

If the vertices A,B,C of a triangle ABC have position vectors `(1,2,3),(-1,0,0)(0,1,2)` respectively then find `angle ABC (angle ABC` is the angle between the factors BA and BC).

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We are given the points `A(1,2,3), B(-1,0,0) and C(0,1,2)`.
Also, it is given that `angle ABC` is the angle betwenn the vectors BA and BC.
Here, `vec(BA)=PV of A-PV of B=(hat(i)+2hat(j)+3hat(k))-(-hat(i)+0hat(j)+0hat(k))`.
`=[hat(i)-(-hat(i))+(2hat(j)-0)+(3hat(k)-0)]=2hat(i)+2hat(j)+
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