I am 64 years old and reviewing geometry in preparation for a course on GIS. I may be a little more inquisitive than your average teenager. On page 53 of Head First 2D Geometry copyright 2010 you have a diagram. The second note says the triangles are flipped as well as rescaled. Flipped to me means that the 53 degree angle will be on the left side of the larger triangle. If this is true, it seems that the side of the larger triangle measuring 60 cannot be parallel to the side of the smaller triangle measuring 48. On page 57, you add angles indicating the triangles are similar. This was not clear in the criteria on page 53. In addition, if the triangles are congruent, the sketch is wrong. The apex of the triangles is not the same to my eye (not quite anal enough to find my protractor). One other part of the diagram bothers me. The measure of the top line is 120. The measure of the bottom line is more than 120 because there is space on either side of the triangles.
I can work around this, but please let me know how I am to know that the 60 side is parallel to the 48 side. What does "flipped" mean in this context?
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I checked with the authors of this book, and one of them said, "I think the word 'flipped' on page 53 is a mistake, as the images haven't been flipped, just rescaled. I agree that the sketch doesn't accurately reflect the measurements."
I hope that helps clarify things.
In case it's helpful, you can check the book's errata. There's one confirmed errata here:
And a few unconfirmed errata (including the issue you noted) here:
If you spot any other issues with the book, feel free to note them here:
All the best,