1.

If `veca=hati-2hatj+3hatk, vecb=2hati+3hatj-hatk` and `vecc=rhati+hatj+(2r-1)hatk` are three vectors such that `vecc` is parallel to the plane of `veca` and `vecb` then`r` is equal to,A. `1`B. `0`C. `2`D. `-1`

Answer» Correct Answer - B
It is given `vecc` is parallel to the plane of `veca` and `vecb`
`:.vecc_|_vecaxxvecb`
`impliesvecc(vecaxxvecb)=0implies[(veca, vecb, vecc)]=0`
`implies|(1,-2,3),(2,3,-1),(4,1,2r-1)|=0`
`implies(6r-2)+2(5r-2)+(6-9r)=0implies7r=0impliesr=0`.


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