This question is incomplete because the options were not properly written.
Complete Question
Which of the following applies the law of cosines correctly and could be solved to find m∠E? ANSWERS:
A) cos E = 31²+ 39² – 2(31)(39)
C) 56² = 39² – 2(39) ⋅ cos E
D) 56² = 31² + 39² – 2(31)(39) ⋅ cos E
Answer:
D) 56² = 31² + 39² – 2(31)(39) ⋅ cos E
Step-by-step explanation:
From the above diagram, we see are told to apply the law of cosines to solve for m∠E i.e Angle E
The formula for the Law of Cosines is given as:
c² = a² + b² − 2ab cos(C)
Because we have sides d , e and f and we are the look for m∠E the law of cosines would be:
e² = d² + f² - 2df cos (E)
e = 56
d = 39
f = 31
56² = 39² + 31² - (2 × 39 × 31) × cos E
Therefore, from the above calculation and step by step calculation, the option that applies the law of cosines correctly and could be solved to find m∠E
Is option D: 56² = 31² + 39² – 2(31)(39) ⋅ cos E
. Therefore, you get the equation 
. This is equal to 72, so he missed 3 points, or 75-72 points. 