1. **Problem 1.a:** In parallelogram ABCD, given that angle \(\angle DAB = 60^\circ\), find angle \(\angle C\). 2. **Formula and properties:** In any parallelogram, opposite angles are equal, and adjacent angles are supplementary (sum to \(180^\circ\)). 3. **Step-by-step solution:** 1. Given \(\angle DAB = 60^\circ\). 2. Since adjacent angles are supplementary, \(\angle DAB + \angle ABC = 180^\circ\). 3. Calculate \(\angle ABC = 180^\circ - 60^\circ = 120^\circ\). 4. Opposite angles are equal, so \(\angle C = \angle ABC = 120^\circ\). 4. **Final answer:** \(\boxed{120^\circ}\). 5. **Problem 1.b:** Describe the properties of a rhombus. 6. **Properties of a rhombus:** 1. All four sides are equal in length. 2. Opposite angles are equal. 3. Adjacent angles are supplementary. 4. Diagonals bisect each other at right angles (90°). 5. Diagonals bisect the angles of the rhombus. 6. It is a special type of parallelogram with equal sides. 7. These properties make the rhombus a unique quadrilateral with both parallelogram and kite characteristics.