$\"\"$

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(a) $\"\"$

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The trigonometric function is $\"\"$ .

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Pythagorean identity : $\"\"$

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$

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Take square root of each side.

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$\"\"$ $\"\"$

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$\"\"$ .

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$\"\"$

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(b) $\"\"$

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Trigonometric identity : $\"\"$ .

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$\"\"$ .

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$\"\"$

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(c) $\"\"$

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Reciprocal identity : $\"\"$ .

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$\"\"$ .

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$\"\"$

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(d) $\"\"$

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Co-function identity : $\"\"$ .

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$\"\"$ .

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$\"\"$

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(a) $\"\"$ ,

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(b) $\"\"$ ,

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(c) $\"\"$ , and

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(d) $\"\"$ .