Find the value of Arccos(-1/2)

arccos(- 1 / 2)

Assume y = arccos(- 1 / 2).

cos y = – 1 / 2 with 0 ≤ y ≤ Π (Cos Theorem) … (1)

Cos (π / 3) = 1 / 2 (Use table of Special Angles)

And also, cos(Π – x) = – cos x.

cos (π – π/3) = – 1 / 2 …(2)

Compare statement 1 with statement 1

y = Π – Π / 3 = 2 Π /3

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