## Geometry: Common Core (15th Edition)

$m∠1$ = $30^{\circ}$
The measures of the three angles of a triangle equal $180^{\circ}$; therefore, if we have the measure of the other two angles, we can figure out the measure of $∠1$. Let $x$ equal $m∠1$: $33 + 117 + x = 180$ Add the constants on the left side together: $150 + x = 180$ Subtract $150$ from each side to solve for $x$: $x = 30$ $m∠1$ = $30^{\circ}$