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Evaluate each of the following:
cos–1(cos 12)
cos–1(cos x) = x
Provided x ϵ [0,π] ≈ [0,3.14]
And in our equation x is 4 which does not lie in the above range.
We know cos[2nπ – x] = cos[x]
∴ cos(2nπ – 12) = cos(12)
Here n = 2.
Also 4π–12 belongs in [0,π]
∴ cos–1(cos 12) = 4π–12