DEFINITION: Tessellation is a repeating pattern of distinct shapes that tiles or covers a surface WITHOUT ANY GAPS OR OVERLAPS.

Lesson 103 - Finding the Unit:

I picked the second one (unit) as my answer then I saw you said the correct answer was the third one (unit).

But that answer would cause the next horizontal and the next vertical units to share a triangle (the lower triangle on the next horizontal unit is the same as the top triangle on the next vertical unit.)

Could you please explain how this complies with the definition of a tessellation?

Thanks,
Liam

From the dad (Dave): I found your diagram a little confusing because the pattern of dodecagons & triangles on the right side are not complete units (they are each missing one triangle). Likewise, the dodecagons on the left side each depict an extra triangle. I think it would have been clearer for the teaching purposes for this lesson to show the tessellation example with complete units only. Either that or I think you should mention that you the units might be incomplete around the edges of the portion of the tessellation that you show. We spent about 30 minutes trying to understand this. Once I understood this, it helped us to pick out the units.

On the worksheet, nos. 1-3 depict only complete units. However, nos. 4-8 depict broken units around the edges.

Also, I don't see how your first answer option for no. 7 can be correct (you leave the star out, but wouldn't that make the star a gap?)

Note: I agree with my son's reasoning above. Maybe some of my confusion stemmed from whether the wrong answer was given for that question.

Dear Liam and Dad Dave,


I agree with you that either the figures should use complete units or a note be added.


Also, the answer to #7 should include the star.


I will change the lessons accordingly and post the corrections on our Corrections page in about a week (I'm out of the country at the moment.). Thanks so much for pointing this out. Sorry for the confusion.


Joan Cotter