The area of the triangle whose vertices are
`A(1,-1,2),B(2,1-1)C(3,-1,2)` is …….

Answer

`sqrt13`

Explanation

Aera of `triangleABC = 1/2 |vec(BA)xxvec(BC)|`
`vec(BA)= -hati-2hatj + 3hatk`
`vec(BC)=hati-2hatj +3hatk`
`Area=1/3|{:(hati,hatj,hatk),(-1,-2,3),(1,-2,3):}|=1/2|6hatj+4hatk|`
`|3hatj +2hatk|`
`sqrt(9+4) = sqrt13`