Question

In a ∆ABC, if c² + a² – b² = ac, then ∠ B=

• A. $\frac{\pi}{6}$
• B. $\frac{\pi}{4}$
• C. $\frac{\pi}{3}$
• D. None of these

Answer 1

Answer: (C)

$\frac{\pi}{3}$

Answer 2

c² + a² –b² = ac

⇒ $\frac{c^{2} + a^{2} - b^{2}}{2ac}$ = $\frac{1}{2}$

⇒ cos B = $\frac{1}{2}$⇒ ∠B = 60⁰