Answer:
C. 12.3
Step-by-step explanation:
We should use Law of Cosines: c² = a² + b² -2abcosC
If that is the case, then EF is a, DF is b, and ∠F is c. We then plug the known variables in:
c² = 12² + 13² - 2(12)(13)cos59°
Plug that into the calc and you should get 12.2313, rounded to 12.3 as your final answer!
