## Geometry: Common Core (15th Edition)

The third angle measures $54.5^{\circ}$.
We know that the three interior angles of a triangle equal $180$. If we are already given two of the angles, we can figure out the third angle. Let us set up the equation to add the three angles together. One angle measures $54.5$, and the other measures $71$. Let $x$ be the measure of the last angle: $54.5 + 71 + x = 180$ Let's add the constants together on the left side of the equation to simplify: $125.5 + x = 180$ To solve for $x$, subtract $125.5$ from each side of the equation: $125.5 - 125.5 + x = 180 - 125.5$ Subtract to simplify: $x = 54.5$ The third angle measures $54.5$.