Note that Cosine law can be used if three sides of the triangle are given in order to get the angles.
For example, in getting the measurement of angle C
[tex]\cos C=\frac{a^2+b^2-c^2}{2ab}[/tex]
Then take the arccos to get the angle C.
From the problem, we have :
We need to find the measurement of angle F using the same formula above.
[tex]\begin{gathered} \cos F=\frac{16^2+12^2-18^2}{2(16)(12)} \\ \cos F=\frac{19}{96} \end{gathered}[/tex]
Taking the arc cosine :
[tex]\begin{gathered} \angle F=\arccos (\frac{19}{96}) \\ \angle F=78.58 \end{gathered}[/tex]
The answer rounded to the nearest 10th is
