$\"\"$

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Each pair of base angles of an isosceles trapezoid are congruent.

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So, $\"\"$ .

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Since $\"\"$ , $\"\"$ are supplementary.

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Since $\"\"$ , $\"\"$ are supplementary.

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$\"\"$ (Supplement theorem)

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

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$\"\"$ (Combine like terms)

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$\"\"$ (Add 4 to each side)

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$\"\"$ (Divide each side by 23) $\"\"$

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Use $\"\"$ to detemine the measures of base angles.

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$\"\"$ (Given) $\"\"$

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$\"\"$ (Substiute $\"\"$ ) $\"\"$

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

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Because $\"\"$ , $\"\"$ and $\"\"$ . $\"\"$

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Measures of base angles are $\"\"$ and $\"\"$ .