.You can compute the length of BC by (1) solvingThe sum of the angles that make up each of theoverlapping triangles within the quadrilateral is asfollows:The sum of the closing errors for the four trianglesis (09 + 01 + 07 + 01), or 18 seconds. The averagetriangle closure for the four triangles, then, is 18/4, or04.5 seconds. For third-order triangulation, themaximum average triangle closure is 05 seconds;therefore, for the third-order work this closure wouldbe acceptable.Base Line DiscrepancyIf AD is the base line in figure 15-28, then BC wouldbe the adjacent baseline.assume that the baselineAD measures 700.00 feet and compute the length of BCon the basis of the angles we have adjusted. These anglesnow measure as follows:The natural sine of each of these angles is asfollows:triangle ABD for AB and triangle ABC for BC and (2)solving triangle ACD for DC and triangle DBC for BC.Using the law of sines and solving triangle ABD forside AB, we haveSolving triangle ABC for side BC, we haveSolving triangle ACD for side CD, we haveSolving triangle DBC for side BC, we have15-38