$\"\"$

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The equation is $\"\"$ .

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Apply formula: $\"\"$ .

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$\"\"$

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Subtract 21 from each side.

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$\"\"$

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$\"\"$

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$\"\"$

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Compare the equation with $\"\"$ .

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a = 1, b = $\"\"$ and c = $\"\"$ .

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Apply quadratic formula: $\"\"$ .

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$\"\"$ (Replace a with 1, b with $\"\"$ , and c with $\"\"$ ) $\"\"$

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Product of two same sings is positive.

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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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$\"\"$

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$\"\"$ $\"\"$

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The solutions are $\"\"$ .