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JEE Main20202 Sep 2020Morning ShiftMathematicsVector AlgebraActual

Let a → , b → and c → be three unit vectors such that a → - b → 2 + a → - c → 2 = 8 . Then a → + 2 b → 2 + a → + 2 c → 2 is equal to

Correct answer

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Step-by-step solution

a → = b → = c → = 1 a → - b → 2 + a → - c → 2 = 8 ⇒   1 + 1 - 2 a → · b → + 1 + 1 - 2 a → · c → = 8 ⇒    a → · b → + a → · c → = - 2 Now a → + 2 b → 2 + a → + 2 c → 2 = a → 2 + 4 b → 2 + 4 a → · b → + a → 2 + 4 c → 2 + 4 a → · c → = 2 a → 2 + 4 b → 2 + 4 c → 2 + 4 a → · b

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