frac{4^2 + 6.9^2 - 4.2^2}{2 \times 4 \times 6.9}\) \(\cos{y} = 0.8327898 \dotsc\). Do not round this answer yet. To calculate the angle use the inverse cos button on the calculator (\(\cos^{-1}\)).

To calculate the angle use the inverse sin button on the calculator \(x = 25.4^\circ\). The cosine rule is: \(a^2 = b^2 + c^2 - 2bc \cos{A}\). This version is used to calculate lengths.