## Geometry: Common Core (15th Edition)

$m \angle 1 = 90^{\circ}$ $m \angle 2 = 60^{\circ}$ $m \angle 3 = 60^{\circ}$ $m \angle 4 = 30^{\circ}$
Diagonals of rhombuses bisect pairs of opposite angles, so $m \angle 4$ is also $30^{\circ}$. Diagonals of rhombuses cross each other at right angles, so $m \angle 1 = 90^{\circ}$. Let's look at one of the smaller triangles. We have $m \angle 1 = 90^{\circ}$ and the angle that measures $30^{\circ}$; therefore, we only have to find $m \angle 2$. The interior angles of a triangle add up to $180^{\circ}$: $m \angle 2 = 180 - (90 + 30)$ Evaluate parentheses first, according to order of operations: $m \angle 2 = 180 - (120)$ Subtract to solve: $m \angle 2 = 60^{\circ}$ Now that we know $m \angle 2$, we also know $m \angle 3$ because the diagonal bisected the angle containing $\angle 2$ and the angle containing $\angle 3$. These bisected angles are opposite angles, so $m \angle 3$ is the same as $m \angle 2$. $m \angle 3 = 60^{\circ}$