1.

The position vectors of vertices of a Delta ABC are 4hat(i)-2hat(j), hat(i)-3hat(k) and -hat(i)+5hat(j)+hat(k) respectively, then angle ABC is equal to

Answer»

`pi/6`
`pi/4`
`pi/3`
`pi/2`

SOLUTION :Here, `AB=-3 hati+6hatj-3hatk`
`BC = -2 hati+hatj+4hatk`
and `AB*BC=6+6-12=0`
`RARR""/_ABC=pi/2`


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