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Measurement Session 4: Notes
 
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Notes for Session 4, Part C


Note 6

How To Use Geo-Logo
If you are using Geo-Logo instead of the Interactive Activity, the following are the instructions on how to use it: Direct the cursor (in the form of a "turtle") around the computer screen using commands that move it forward (fd), back (bk), right (rt), and left (lt). Each command requires an input or number that indicates the distance the turtle will move (e.g., fd 30, bk 45) or the amount of the turn it will make (e.g., rt 90, lt 180). The inputs for the fd and bk commands are lengths, and the inputs for the rt and lt commands are degrees.

When drawing a shape in Geo-Logo, the commands rt and lt instruct the turtle to turn a number of degrees in a set direction. This can be confusing, because these commands indicate the amount of turn of the exterior angle, rather than the interior angle. For example, the commands fd 20 rt 30 fd 20 draw an obtuse angle that measures 150 degrees; the commands fd 20 rt 120 fd 20 draw an angle that measures 60 degrees. Notice that the amount of turn (exterior angle) and the resulting angle (interior angle) are supplementary -- they sum to 180 degrees.

Another command that is very useful is the repeat command, which allows you to repeat a command or a sequence of commands any number of times. For example, try the following commands: repeat 6 [fd 70 lt 150]. Experiment using the Geo-Logo commands prior to starting to draw the shapes in Problem C1.

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Note 7

If you are working in groups, review and discuss Problem C3. For each of the polygons drawn in Problem C1, have group members add the amount of turns that were used to draw the shape and bring the turtle back to its starting position. Discuss the following questions: What is the total sum of the turtle turns for each polygon? (Or, in other words, what is the sum of the exterior angles of these polygons?) If, when drawing the polygons, the turtle had not gone forward but rather had stayed in one spot, what figure would the turtle have drawn?

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