A triangle has sides 3 cm, 5 cm and 7 cm. What is the angle between the sides of 3 cm and 5 cm?
Answer and explanation
Correct answer: A. 120°
- Step 1: By the cosine law, c² = a² + b² - 2ab cos C.
- Step 2: cos C = (9 + 25 - 49) / (2 x 3 x 5) = -1/2, so C = 120°.
Answer
120°.
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