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JEE Main202125 Jul 2021Evening ShiftMathematicsVector AlgebraActual

If a → and b → are unit vectors and a → + 3 b → is perpendicular to 7 a → - 5 b → and a → - 4 b → is perpendicular to 7 a → - 2 b → , then the angle between a → and b → (in degrees) is _________.

Correct answer

0

Step-by-step solution

We have, a → + 3 b → ⊥ 7 a → - 5 b → Therefore, a → + 3 b → · 7 a → - 5 b → = 0 ⇒ 7 a → 2 - 15 b → 2 + 16 a → · b → = 0             … 1 and a → - 4 b → · 7 a → - 2 b → = 0 ⇒ 7 a → 2 + 8 b → 2 - 30 a → · b → = 0           … 2 From 1 and 2 , we get 2 a → cos θ = b → ∴ &#160

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