$\"\"$

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(a)

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The expression is $\"\"$ .

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Using sum and difference formulas: $\"\"$ .

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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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(b)

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The expression is $\"\"$ .

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$\"\"$

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$\"\"$ .

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$\"\"$

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

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