Answer:
Cosθ = -0.07
Step-by-step explanation:
Law of Cosines
c² = a² + b² - 2abCosC
The givens
a = 7, b = 8, c = 11, C = θ
Plug into the formula
11² = 7² + 8² - 2(7)(8)Cosθ
Square
121 = 49 + 64 - 112Cosθ
Combine terms
121 = 113 - 112Cosθ
Subtract 113 from both sides
8 = -112Cosθ
Divide both sides by -112
-0.07142857143 = Cosθ
Round to 2dp
Cosθ = -0.07
