81 Test file number 153

  81.1 Problem number 18
  81.2 Problem number 19
  81.3 Problem number 20
  81.4 Problem number 21
  81.5 Problem number 22
  81.6 Problem number 23
  81.7 Problem number 24
  81.8 Problem number 25
  81.9 Problem number 26
  81.10 Problem number 27
  81.11 Problem number 28
  81.12 Problem number 29

Test folder name:

test_cases/5_Inverse_trig_functions/5.3_Inverse_tangent/153_5.3.7_Inverse_tangent_functions