Hello,

Let y be cot x.

The problem is now to solve

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Between 0° and 180° the cot function is decreasing. So there is one and only one value verifying y=0 in this interval. And the function is pi(180)-periodic.

cot x = 0 when x=90° or 270° (because cot x = cos(x)/sin(x))

We know that and

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By the property of the periodicity, too

Solutions are