$\"\"$

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The trigonometric function : $\"\"$ .

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(a) $\"\"$ .

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Supplements of trigonometric functions : $\"\"$ .

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$\"\"$ .

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$\"\"$

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(b) $\"\"$

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Periodicity of trigonometric functions : $\"\"$ .

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$\"\"$ .

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$\"\"$

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(a) The value of $\"\"$ .

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(b) The value of $\"\"$ .