Question

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Answer 1

Cotangent is A/O. Cosine is A/H. Cosecant is H/O. To prevent division by zero, O must not be zero and H must not be zero. H is never zero, but O is zero at angles of 0, +/-pi, +/-2pi, etc. So the domain of validity = {x : x not = 0, +/-pi, +/-2pi, ...}

Answer 2

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