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MHT CET202124 Sep 2021Morning ShiftMathematicsVector AlgebraActual

If a =2 i +3 j - k , b =- i +2 j -4 k and c = i + j -2 k , then ( a b ) ( a c )=

Options

  1. A-30
  2. B84
  3. C70
  4. D984

Correct answer

C. 70

Step-by-step solution

aligned & a b = | array ccc i & j & k 2 & 3 & -1 -1 & 2 & -4 array |= i (-10)- j (-9)+ k (7)=-10 i +9 j +7 k & a c = | array ccc i & j & k 2 & 3 & -1 1 & 1 & -2 array |= i (-5)- j (-3)+ k (-1)=-5 i +3 j - k & ( a b )( a c )=(-10 i +9 j +7 k ) (-5 i +3 j - k )=50+27-7=70 aligned

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