$\"\"$

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(a) The function is $\"\"$ .

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Definition of the hyperbolic function $\"\"$ .

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$\"\"$

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$\"\"$ .

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$\"\"$

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(b) The function is $\"\"$ .

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$\"\"$

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Definition of the hyperbolic function $\"\"$ .

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$\"\"$

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$\"\"$

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$\"\"$

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

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$\"\"$ .

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$\"\"$

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(a) $\"\"$ .

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(b) $\"\"$ .