It is rare but does happen that errors pop up in our textbooks. One of my students (finger in photo) pointed out the issue in our Geometry text. Apparently, the image of the arrowhead-like figure had two angles of the same measure that should have been known by double-tick marks. Unfortunately, that part of the image was about half a centimeter too low and it became confusing to students. We made sure to fix this issue on our smartboard to show students what it should look like.
I am a math teacher in the New York Department of Education. I infuse technology and real-world problems into my curriculum in order to prepare my students for the future. I would love for people across the country to recognize we teachers can't do it alone. If you don't believe me, come visit my classroom!