Question

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17. Find the measure of DE

A) 14.5
B) 13.4
C) 12.3
D) 15.9

Answer 1

C. 12.3

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!