$\"\"$

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(a).

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The trigonometric function is $\"\"$ .

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$\"\"$ (Substitute $\"\"$ for $\"\"$ )

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$\"\"$ (Since $\"\"$ )

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$\"\"$

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$\"\"$ radians

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$\"\"$ radians.

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$\"\"$

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(b).

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The trigonometric function is $\"\"$ .

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$\"\"$ (Substitute $\"\"$ for 1)

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$\"\"$ (Since $\"\"$ )

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$\"\"$

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$\"\"$ radians

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$\"\"$ radians.

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$\"\"$

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(a) The angle $\"\"$ or $\"\"$ radians.

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(b) The angle $\"\"$ or $\"\"$ radians.