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AP EAMCET · Maths · Trigonometric Ratios & Identities

In triangle \(A B C\) if \(\cos A \cos B+\sin A \sin B \sin C=1\), then \(\sin A+\sin B+\sin C=\)

  1. A \(\frac{2+\sqrt{3}}{2}\)
  2. B \(1+\sqrt{2}\)
  3. C \(\frac{2 \sqrt{3}-1}{2}\)
  4. D \(\frac{3+\sqrt{3}}{2}\)
Verified Solution

Answer & Solution

Correct Answer

(B) \(1+\sqrt{2}\)

Step-by-step Solution

Detailed explanation

\(\cos A \cos B+\sin A \sin B \sin C=1 \Rightarrow (\cos A \cos B+\sin A \sin B) + \sin A \sin B (\sin C - 1)=1\) \(\Rightarrow \cos(A-B) + \sin A \sin B (\sin C - 1)=1\) Since \(\cos(A-B) \le 1\) and \(\sin A > 0, \sin B > 0, \sin C \le 1 \Rightarrow \sin C - 1 \le 0\), it must…