In a triangle, the lengths of the two sides are 5cm and the angle between them is 120 degrees, find the length of the 3rd side.
| December 7, 2020 | education
Cosine theorem:
a ^ 2 = b ^ 2 + c ^ 2-2bc * cosA
a ^ 2 = 5 ^ 2 + 6 ^ 2-2 * 5 * 6 * cos120 = 25 + 36 -60 * (- 0.5) = 61 + 30 = 91
a ^ 2 = 91
a = √91
Answer: √91.
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