Constructing Shapes in Geometry

Lately in class we have been learning geometry. One part of this that students often have difficulty with is constructing shapes using specific angles and side measurements. For example, in the video below, the question posed is to construct a parallelogram called BACD so that

• AC = BD = 5cm
• BA = DC = 2cm 
• angle ABD = 120 degrees and angle BDC = 60 degrees

When I teach students how to construct these shapes, I first ask them to make a sketch of the shape they are supposed to be drawing if possible. In this case, they should make a sketch of a parallelogram. They also need to stop and think at this moment about what they know about a parallelogram:

• opposite sides have to be equal and parallel
• opposite angles have to be equal 

At this point, students can sketch the parallelogram and  place the labels in the appropriate places. At this time, they can ensure they have the correct lengths and angles in all the right places as well, before they start actually drawing their shape using a ruler and protractor. To see how to draw the shape accurately, please watch the video below.