Using the cosine rule, BC = √(115² + 80² - 2(115)(80)(cos 72) ≈ 118.1 m (1 decimal place).
If we are given a triangle with two known sides and an included angle, the cosine rule that can be used to find the side opposite to the given angle is: a = √(b² + c² - 2bc(cos A)
We are given the following:
Plug in the values
BC = √(115² + 80² - 2(115)(80)(cos 72)
BC ≈ 118.1 m (1 decimal place)
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