$\"\"$

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The expression is $\"\"$

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if $\"\"$ ,where b,d $\"\"$

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$\"\"$

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$\"\"$ (Multiply numerators: $\"\"$ )

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$\"\"$ (Multiply denominators: $\"\"$ )

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$\"\"$ (40 can be written as $\"\"$ )

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$\"\"$ (Cancel common terms) $\"\"$

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The product is $\"\"$ .