# Discrete Dots and the TI-83

Spike Clancy (hclancy@dimacs.rutgers.edu)

General Information
This lesson is based on Adi Shamir's talk on "Cryptography Without Computers" and the UCSMP Geometry book definition of discrete points or pixels. By using a TI-83 calculator we can hide information.

Category
This lesson can be used in geometry, Algebra I or II, and courses in discrete mathematics or cryptography.

Grades 9 - 12 (also 7 & 8 with revisions)

Activity 1
Hiding Informations with the TI-83

Suggested Materials
TI-83 calculators
TI-83 view screen

Procedure
1. Draw face or message on the TI-83 using <Graph> <2nd> <Draw> Circle.
2. Draw circle for face and eyes.
3. <2nd> <Draw> <Pen> to draw mouth.
4. <2nd> <Draw> >> <Sto> <1> Store pic in 1.
5. To recall the picture <2nd> <Draw> >> <2>.
6. Use <2nd> and hold down <^> to darken screen and hide picture.
7. Use <2nd> and hold down <v> to regain hidden picture.
8. To hide a text use <2nd> <Draw> ??? text.
9. Write out text and follow directions for hiding pictures.

Hints:
1.If mistakes are made hit <2nd> <Draw> <1> "ClrDraw" and start over again.
2. Use <2nd> <Format> and turn axes off.

References
UCSMP Geometry, Scott Foresman (c)1997