Problem
a) Show that $\angle D O A=105^{\circ}$ b) Show that the length of DA is $127 \mathrm{~m}$ (to the nearest metre) c) Hence, find the perimeter and area of the entire block of land $A B C D$
Solution
Step 1 ：\(\angle AOC = 180^\circ - \angle BOC = 180^\circ - 120^\circ = 60^\circ\)
Step 2 ：\(\angle AOD = 180^\circ - \angle AOC = 180^\circ - 60^\circ = 120^\circ\)
Step 3 ：\(\angle DOA = 360^\circ - \angle AOD - \angle DAO = 360^\circ - 120^\circ - 135^\circ = 105^\circ\)
