## Geometry: Common Core (15th Edition)

Use the definition of a linear pair to write and solve equations. Solve for y: $(y+x)+(y-x)=180\longrightarrow$ a linear pair is supplementary $2y=180\longrightarrow$ combine like terms $y=90\longrightarrow$ division property of equality Substitute and solve for x: $2x+(y+x)=180\longrightarrow$ a linear pair is supplementary $3x+y=180\longrightarrow$ combine like terms $3x+90=180\longrightarrow$ substitute $3x=90\longrightarrow$ subtraction property of equality $x=30\longrightarrow$ division property of equality Substitute to find the measure of each angle. $2x=2(30)=60$ $y+x=90+30=120$ $y-x=90-30=60$