Answer: D. Law Of Cosines
Step-by-step explanation: A law in trigonometry: the square of a side of a plane triangle equals the sum of the squares of the remaining sides minus twice the product of those sides and the cosine of the angle between them.
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The sum of the interior angle of the triangle is 180 degrees. Then by the sine rule, angle E can be determined. Then the correct option is A.
Trigonometry deals with the relationship between the sides and angles of a right-angle triangle.
For triangle DEF, the length of side e and the measures of angles D and F are known.
We know that the sum of the interior angle of the triangle is 180 degrees. Then the angle E can be determined.
Hence the sine rule is easy to apply.
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