Monday, January 25, 2021

The Sine of 35º is a Constant

   It is well known that the ratio of the circumference to the diameter of any circle equals Pi (π).
   The circle could be as small as that of an atom or as large as a circle in space with a diameter of one light year. In all such cases the ratio of the circumference to the diameter is constant. The ratio of the circumference to the diameter in the red circle is the same for the yellow and black circles.

   Good math teachers will have students measure the circumference of several circular objects (like circular lids) as accurately as possible to establish the belief that the ratio of the circumference to the diameter of any circle is Pi.
   I remember being taught the sine, cosine, and tangent trigonometry functions from a single textbook diagram of a right triangle. No effort was made to show that the ratios were constant for any given angle no matter the size of the right triangle containing the given angle. 

   This project has the mouse draw a right triangle with angles equal to 35º, 90º, and 55º. The mouse first draws the hypotenuse of the right triangle a random number of steps. The mouse turns to the right and draws the perpendicular to the base of the triangle. The mouse then turns right through 90º and draws the side adjacent to the 35º angle. The program then computes and displays the sine(35º) using the known lengths of the hypotenuse and opposite side. The program repeats’ this process 9 more times, producing a series of right triangles that demonstrate the sine(35º) is a constant 0.57735… for all of the ten right triangles.
   The project can be viewed and downloaded at the following link.
    This is a screen shot of the output of the project.

       Teachers and students might be interested in a free PDF tutorial on the project that can be obtained by emailing

Thursday, January 14, 2021

Scalene Triangle Mouse Using the Law of Cosines

   In the December 21, 2020 post (Coding Math Concepts as Tests of Student Comprehension) I presented the problem of coding a scalene triangle as a challenge considerably tougher than just learning the definition of a scalene triangle and examining a few triangles.
   I felt there was a crudeness to the method I used and even published an Addendum December 23, 2020 (Addendum to Scalene Triangle Mouse I) that 'fixed' the heading problem presented by the go to that drew the third leg. In this post, I offer another method for drawing a scalene triangle that uses the law of cosines taught in s first trigonometry course.

   The method is straight forward and essentially requires coding the angle formulas shown in the following diagram since the program asks the user to set the lengths of the three sides to different values (the definition).

   Teachers and students might be interested in the free PDF file that describes the Scratch program in more detail. If interested, send an email requesting Scalene Triangle Mouse II and I will end you a copy that holds no copyright. I will also send upon request the Word file that can be changed if you don't have Adobe.

Monday, January 11, 2021

Using Lists in Scratch - Singe Die Frequencies

    Scratch is a descendent of the Logo programming language that was developed by Dr. Seymour Papert at the the Artificial Lab at MIT. Logo had elements of the LISP programming language popular at the Lab at that time. LISP is an acronym for LIStProcessing and used data structures called lists. 
   To illustrate the use of lists I've written a PDF document that uses lists to store the frequency of the results of throwing a single die a number of times. Assuming the die is a fair die, the frequency of each of the numbered faces, 1, 2, 3, 4, 5 and 6 should be equal for say 6 throws, 36 throws, and 216 throws. Here is the Scratch script.

   Below is a screenshot of the display produced by the above script for six rolls of a single die. Note that the program does not produce the theoretical values of the frequency of 1 for each of the six possibilities. Bit neither does six rolls of a real die.
   If you are a teacher or a students and would like a free copy of the PDF file that details the building of the script just email your request to
   A more advanced project that uses lists to record the frequency of the sum of a pair of dice for a repeated number of throws will be the topic of a future post.