In triangle PQR, cm, cm and angle . Find the length of QR to 3 significant figures.

Answer and explanation

Correct answer: D. 8.19 cm

  1. Step 1: Use the cosine rule: .
  2. Step 2: .
  3. Step 3: .
Answer
8.19 cm.
Why not the others: 11.4 cm is (forgetting to subtract the cosine term), 9.00 cm is just the length of PR and 16.0 cm is 7 + 9.

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