Discovering Some Properties of Rectangles
Using Geometer's Sketchpad
by David Wise

Note: I recommend that this page be printed out, so that the instructions are easier to follow.

Definition: A rectangle is an equiangular parallelogram

Click here to link to the rectangle sketch needed to carry out the investigation.

By definition, a rectangle is a parallelogram, so you should be able to determine the measure of each angle of a rectangle using properties of parallelograms and quadrilaterals. If you have difficulty, complete the following two steps and complete the conjecture.

  1. Use the measure menu to find the measure of each angle of the rectangle.
    a. Remember to use the shift key when selecting more than one object.
    b. Remember that the points must be selected a counterclockwise order to obtain a positive angle measure in directed degrees.
  2. Compare the measure of the 4 angles.
    a. Click and drag any vertex.
    b. Click and drag any side.
    c. What is the measure of each angle? Complete the conjecture.

C-59 The measure of each angle of a rectangle is_________________________________.

C-60 The diagonals of a rectangle are__________________________________________.

If you have any questions while trying to complete this investigation, or suggestions that would be useful, especially for use at the high school level, please send e-mail to

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