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CUET · MATHS · PYQ PAPER 2025

If \( \vec{a}\) is a unit vector and \((\vec{x}-\vec{a}) \cdot(\vec{x}+\vec{a})=15\), then the value of \(|\vec{x}|\) is :

  1. A 0
  2. B 16
  3. C 4
  4. D 2
Verified Solution

Answer & Solution

Correct Answer

(C) 4

Step-by-step Solution

Detailed explanation

\((\vec{x}-\vec{a}) \cdot(\vec{x}+\vec{a})=15\) \(|\vec{x}|^2 - |\vec{a}|^2 = 15\) \(|\vec{x}|^2 - 1^2 = 15\) \(|\vec{x}|^2 = 16\) \(|\vec{x}| = 4\)
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