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CUET · MATHS · PYQ PAPER 2025

If \(\vec{a}+\vec{b}+\vec{c}=\overrightarrow{0}\) and \(|\vec{a}|=5,|\vec{b}|=3,|\vec{c}|=7\), then the acute angle between \(\vec{a}\) and \(\vec{b}\) is

  1. A \(\frac{\pi}{4}\)
  2. B \(\frac{\pi}{2}\)
  3. C \(\frac{\pi}{6}\)
  4. D \(\frac{\pi}{3}\)
Verified Solution

Answer & Solution

Correct Answer

(D) \(\frac{\pi}{3}\)

Step-by-step Solution

Detailed explanation

\(|\vec{c}|^2 = |\vec{a}+\vec{b}|^2\) \(|\vec{c}|^2 = |\vec{a}|^2 + |\vec{b}|^2 + 2|\vec{a}||\vec{b}|\cos\theta\) \(7^2 = 5^2 + 3^2 + 2(5)(3)\cos\theta\) \(49 = 25 + 9 + 30\cos\theta\) \(49 = 34 + 30\cos\theta\) \(15 = 30\cos\theta\) \(\cos\theta = \frac{1}{2}\)…