$\"\"$

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Let $\"\"$ and $\"\"$ .

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$\"\"$ (Apply Secant theorem)

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$\"\"$ (Substitute $\"\"$ and $\"\"$ )

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$\"\"$ (Multiply each side by 2)

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$\"\"$ (Simplify) $\"\"$

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$\"\"$ (Subtract 2x from each side)

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$\"\"$ (Simplify)

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$\"\"$ (Add 40 to each side)

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$\"\"$ (Simplify) $\"\"$

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$\"\"$ (Divide each side by 8)

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$\"\"$ (Cancel common terms)

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$\"\"$ (Divide: $\"\"$ ) $\"\"$

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The value of $\"\"$ .