write principal value of: (cos-1root3/2 +cos-1(-1/2))

We know that, range of the principal values of cos-1 is 0,π.Let cos-132 = αcos α = 32cos α = cosπ6α =π6 0,π.Let cos-1-12 = βcos β = -12cos β =-cosπ3cos β = cosπ-π3cos β = cos2π3β = 2π3 0,π.Now, cos-132 + cos-1-12 = π6+2π3 = 5π6

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