$\"\"$

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The sequence is $\"\"$

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Find the common difference $\"\"$ .

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$\"\"$ .

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$\"\"$ .

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$\"\"$ .

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$\"\"$

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$\"\"$

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Since the difference is not equal.

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Observe the difference sequence $\"\"$

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Find the second common difference $\"\"$ .

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$\"\"$ .

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$\"\"$ .

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$\"\"$ .

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$\"\"$ .

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Since the second difference are equal, the series is in quadratic equation,

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$\"\"$

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The general form of $\"\"$ -terms of quardatic equation form $\"\"$

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Substitute $\"\"$ and $\"\"$ in the general form.

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$\"\"$

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Substitute $\"\"$ and $\"\"$ in the general form.

\

$\"\"$

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Substitute $\"\"$ and $\"\"$ in the general form.

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$\"\"$

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Solve the equation $\"\"$ and equation $\"\"$

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$\"\"$

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Solve the equation $\"\"$ and equation $\"\"$

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$\"\"$

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$\"\"$

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Solve the equation $\"\"$ and equation $\"\"$

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$\"\"$

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Substitute $\"\"$ in the equation $\"\"$ .

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$\"\"$

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Substitute $\"\"$ and $\"\"$ in the equation $\"\"$ .

\

$\"\"$

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Substitute $\"\"$ , $\"\"$ and $\"\"$ in the general form of quadratic equation.

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$\"\"$

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The $\"\"$ -terms of arthmetic sequence is $\"\"$

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$\"\"$

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The $\"\"$ -terms of arthmetic sequence is $\"\"$ .