$\"\"$

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For a regular octagon, $\"\"$ .

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The measure of an interior angle of a regular n-gon formula is $\"\"$

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$\"\"$ (Substitute 8 for n)

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$\"\"$ (Subtract: $\"\"$ )

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

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

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In a regular octagon each interior angle forms a straight angle with exterior angle at each

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vertex.

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So, interior and exterior angles are supplementary angles.

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$\"\"$ (Angles are supplementary) $\"\"$ ( $\"\"$ ) $\"\"$ (Subtract $\"\"$ from each side) \ \ $\"\"$

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Aplpy commutative property of addition: $\"\"$ .

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$\"\"$

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$\"\"$ (Apply additive inverse property: $\"\"$ )

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$\"\"$ (Apply additive identity property)

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$\"\"$ (Subtract: $\"\"$ ) $\"\"$

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The measure of an interior angle of a regular traingle is $\"\"$ .

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The measure of an exterior angle of a regular traingle is $\"\"$ .