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The points with position vectors `alpha hati+hatj+hatk, hati-hatj-hatk, hati+2hatj-hatk, hati+hatj+betahatk` are coplanar ifA. `(1-alpha)(1+beta)=0`B. `(1-alpha)(1-beta)=0`C. `(1+alpha)(1+beta)=0`D. `(1+alpha)(1-beta)=0` |
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Answer» Correct Answer - A Let `P,Q,R` and `S` be the given points with position vectors `alpha hati+hatj+hatk, hati-hatj-hatk, hati+2hatj-hatk` and `hati+hatj+betahatk` respectively. Then, `vec(QP)=(alpha-1)hati+2hatj+2hatk, vec(QR)=0hati+3hatj+0hatk` and `vec(QS)=0hati+2hatj+(beta+1)hatk` are coplanar. `:.[vec(QP),vec(QR),vec(QS)]=0` `implies|(alpha-1,2,2),(0,3,0),(0,2,beta+1)|=0` `implies (alpha-1)(beta+1)=0implies(1-alpha)(1+beta)=0` |
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