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JEE Main202120 Jul 2021Evening ShiftMathematicsVector AlgebraActual

In a triangle A B C , if | B C → | = 3 , | C A → | = 5 and | B A → | = 7 , then the projection of the vector B A → on B C → is equal to

Options

  1. A19 2
  2. B13 2
  3. C11 2
  4. D15 2

Correct answer

C. 11 2

Step-by-step solution

We have, a → = 3 , b → = 5 , c → = 7 Now, cos θ = a → 2 + c → 2 - b → 2 2 a → c → ⇒ cos θ = 9 + 49 - 25 2 · 3 · 7 ⇒ cos θ = 11 14 Projection of c → on b → = | c → | cos θ = 7 × 11 14 = 11 2

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