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$\"\"$ and $\"\"$ is an even function.

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If $\"\"$ is an even function, then $\"\"$ .

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$\"\"$

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Since $\"\"$

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Hence $\"\"$ .

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Find $\"\"$ .

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Since $\"\"$ is an even function.

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$ .

\

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$\"\"$ .