QUADRILATERAL A polygon (đa giác) is a closed broken line which bounds a portion of a plane. Just as there are classifications for triangles, there are classifications for polygons in general. The classification is determined from the properties of the sides and angles of the polygon under investigation. The following classification of polygons is based on the nature of the angles of the polygon under investigation. (1) If at least one interior angle of a polygon is greater than a straight angle (góc bẹt), the polygon is concave. (2) If each of the interior angles of a polygon is less than a straight angles, the polygon is convex . Only the convex polygons will be consideres in this tex. The following classifications of polygons are based on the number of the sides of the polygon under investigation: (1) A triangle is a polygon havung three sides. (2) A quarilateral is a polygon having four sides. (3) A pentagon is a polygon having five sides. (4) A hexagon is a polygon having six sides. (5) A heptagon is a polygon having seven sides. (6) A octagon is a polygon having eight sides. (7) A nonagon is a polygon having nine sides. (8) A decagon is a polygon having ten sides. CLASSIFICATION OF QUADRILATERAL The most general quadrilateral is irregular in shape. The sum of its interior angles is always 360 degrees. A quadrilateral is classified according to the restrictions placed on its sides and angles A trapezoid (hình thang) is a quadrilateral having two, and only two sides parallel (song song) A rhombus (hình thoi) is a parallelogram with two adjacent sides equal A rectangle (hình chữ nhật) is a parallelogram with one right angle A square (hình vuông) is a rectangle with two adjacent sides equal
