1. **Problem Statement:** Explain the properties of a quadrilateral, specifically focusing on the sum of interior angles and the diagonals forming triangles. 2. **Property (a): Sum of Interior Angles** A quadrilateral has four sides. The sum of its interior angles is always 360°. 3. **Formula and Explanation:** The sum of interior angles of any polygon with $n$ sides is given by: $$\text{Sum} = (n-2) \times 180^\circ$$ For a quadrilateral, $n=4$, so: $$\text{Sum} = (4-2) \times 180^\circ = 2 \times 180^\circ = 360^\circ$$ This means if you add all four interior angles of a quadrilateral, the total will be 360°. 4. **Property (b): Diagonals Form Four Triangles** A quadrilateral has two diagonals that intersect inside the figure. These diagonals divide the quadrilateral into four triangles. 5. **Explanation:** Label the quadrilateral as ABCD with diagonals AC and BD intersecting at point O. The diagonals AC and BD intersect at O, creating four triangles: \triangle AOB, \triangle BOC, \triangle COD, and \triangle DOA. 6. **Summary:** - The sum of interior angles of any quadrilateral is 360°. - The two diagonals intersect and form four triangles inside the quadrilateral. **Final answers:** - Sum of interior angles = $360^\circ$ - Number of triangles formed by diagonals = 4