## Geometry: Common Core (15th Edition)

Let A be the angle, let C be the measure of its complement, and let S be the measure of its supplement. $C+S=114\longrightarrow$ given $(m\angle A+C)+(m\angle A+S)=90+180\longrightarrow$ definition of complement and supplement $2m\angle A+C+S=270\longrightarrow$ combine like terms $2m\angle A+114=270\longrightarrow$ substitution $2m\angle A=156\longrightarrow$ subtraction property of equality $m\angle A=78\longrightarrow$ division property of equality