2. Classification of parallelograms

    Parallelograms are quadrilaterals having opposite sides parallel. We can distinguish four classes:
    1. The rhomboid: it has not right angles and the adjacent sides are unequal.
    2. The rectangle: it has four right angles and the adjacent sides are not equal.
    3. The rhombus: it has no right angles and the sides are equal.
    4. The square: it has four right angles and their sides are equal. It is the regular quadrilateral.

    Look at these pictures and answer these questions:

    3. Review
    Observe the plan of this flat and answer:

   4. Angle Sum of a quadrilateral

   In the quadrilateral ABCD, we draw a diagonal BD and we get two triangles: BCD and ABD. We know that the sum of the angles of a triangle is 180º. We have two triangles and their angles will be 180° x 2 = 360°, that is, A + B + C + D = 360°.
    The sum of the angles of a quadrilateral is 360° or four right angles.

®Arturo Ramo García.-Record of intellectual property of Teruel (Spain) No 141, of 29-IX-1999
Plaza Playa de Aro, 3, 1º DO 44002-TERUEL