Sarkari RiseLogin
NDA 2025 · PYQ · Trigonometry / Triangles · easy

The sides of a triangle ABC are AB = 3 cm, BC = 5 cm and CA = 7 cm. What is ∠B equal to?

Answer

The correct answer is C: 120°. Using cosine rule: cosB = (AB² + BC² - CA²)/(2·AB·BC) = (9 + 25 - 49)/(2·3·5) = -15/30 = -1/2. So B = 120°.

  1. A.60°
  2. B.105°
  3. C.120°✓ Correct
  4. D.150°

Explanation

Using cosine rule: cosB = (AB² + BC² - CA²)/(2·AB·BC) = (9 + 25 - 49)/(2·3·5) = -15/30 = -1/2. So B = 120°.
💡 Practice unlimited NDA PYQs + AI-tracked progress on each topic. Sign up free →

More Trigonometry / Triangles questions

Want more NDA practice?

Free daily 10-Q quiz · adaptive mocks · 49,000+ practice questions (19,000+ verified PYQs) · AI doubt solver in Hindi + English

Sign up freeMore Trigonometry / Triangles practice