Find the exact value of Cosine (StartFraction 5 pi Over 6 EndFraction) cosine (StartFraction pi over 12 EndFraction) + sine (StartFraction 5 pi Over 6 EndFraction) sine (StartFraction pi Over 12 EndFraction)

Afarmer has a large field that is x feet in length. he wants to fence in a rectangular section in the middle of the field , leaving a length of 100 feet of open field behind each end of the fenced rectangle.he also wants the width of the fenced-in space to be 100 feet less than its length. find the expressions to represent the length and width of the fenced section of the field