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JEE Main202125 Jul 2021Evening ShiftMathematicsVector AlgebraActual

If a → = 2 , b → = 5 and a → × b → = 8 , then a → · b → is equal to:

Options

A6
B4
C3
D5

Correct answer

A. 6

Step-by-step solution

We have, a → = 2 , b → = 5 and a → × b → = 8 Now, a → × b → = a → b → sin θ = 8 ⇒ sin θ = ± 4 5 ∴   a → · b → = a → b → cos θ = 10 . ± 3 5 = ± 6 ⇒ a → · b → = 6 .

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