+14913 The principal value is
arc cos 0.1 = 84.3°
but also
cos -635.7° ≈ 0.1
cos -275.7° ≈ 0.1
cos 84.3° ≈ 0.1
cos 444.3° ≈ 01
!
+9519 The principal value is always between \(0^{\circ} - 90^{\circ}\)
So 84.3\(^{\circ}\) is definitely the correct answer.
+36916 Agree, mostly...... the principal value for inverse COS is between 0 and pi/2 (inclusive) for POSITIVE values of COS.
FWIW.
