What I Know Write check mark ( if the statement is correct and cross mark (X) if it is not on the blank. 1. A triangle is a closed figure with three sides and three angles 2. Triangles and quadrilaterals have the same number of sides. 3. The sum of internal angles of triangles and quadrilaterals is 180 4. A quadrilateral is a 4-sided polygon 5. A polygon is a closed figure formed by 3 or more line segment​