If a supplement of an angle has a measure 78 less than the measure of the angle what are the measures of the angles?

Suppose the angle is x

then its supplement is 180 - x

so 180 - x = x - 78

that is, 258 = 2x or x = 258/2 = 129

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Angle + Supplement = 180

Angle = Supplement + 78

Solve for the system of equations...

Angle + Supplement = 180

Angle - Supplement = 78

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2 Angle = 258

Angle = 129

Supplement = 51