$\"\"$

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The trigonometric function is $\"\"$ .

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(a) Solve $\"\"$ .

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$\"\"$

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$\"\"$

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but $\"\"$

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$\"\"$

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$\"\"$ , where $\"\"$ is integer.

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$\"\"$

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(b) $\"\"$ for interval $\"\"$

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$\"\"$

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$\"\"$

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Substitute the values in the interval $\"\"$

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$\"\"$ is true for $\"\"$ .

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$\"\"$ is true for $\"\"$ .

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$\"\"$ is false for $\"\"$ .

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$\"\"$ is false for $\"\"$

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$\"\"$ is false for $\"\"$

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For all positive angles $\"\"$ the function $\"\"$ has positive values.

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So false all positive angles.

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$\"\"$ in $\"\"$ .

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$\"\"$

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(a) $\"\"$ , where $\"\"$ is integer.

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(b) $\"\"$ .