## Geometry: Common Core (15th Edition)

The diagram shows that $\angle BDR$ is a right angle. The Angle Addition Postulate tells us that $\angle BDJ$ and $\angle JDR$ are complementary. $(7y+2)+(2y+7)=90$ combine like terms $9y+9=90$ subtract 9 from each side $9y+9-9=90-9$ $9y=81$ divide each side by 9 $9y\div9=81\div9$ $y=9$