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To explore the properties of a parallelogram, we start by considering a general parallelogram. To draw it, we can use a dynamic geometry software. Remember that a parallelogram is a quadrilateral with both pairs of opposite sides parallel.
To find the properties, first we will find the side lengths, then the angle measures, and finally we will use the diagonals of the parallelogram.
The opposite sides of a parallelogram are congruent. |
The consecutive angles of a parallelogram are supplementary. |
These latter relations lead us to write a third property of parallelograms.
The opposite angles of a parallelogram are congruent. |
Let's draw the diagonals of the parallelogram, and let's label its intersection point.
Since AD∥BC and BD and AC are transversals, by the Alternate Interior Angles Theorem, we get that ∠BDA≅∠DBC and ∠CAD≅∠ACB.
The latter fact leads us to write the last property of parallelograms.
The diagonals of a parallelogram bisect each other. |