1. The problem asks to identify the type of angles labeled $a$ and $b$ based on their position in the diagram. 2. Important angle definitions: - Complementary angles sum to $90^\circ$. - Supplementary angles sum to $180^\circ$. - Vertical angles are opposite angles formed by two intersecting lines and are equal. - Adjacent angles share a common side and vertex. 3. Since $a$ and $b$ are on opposite sides of the horizontal line and formed by the intersection of two lines, they are opposite angles. 4. Opposite angles formed by intersecting lines are called vertical angles. 5. Therefore, angles $a$ and $b$ are vertical angles.