Was enjoying this book until in chapter 4 xy-Coordinate Plane it advises using the Pythagorean Theorem to determine if points on a graph make an isoceles triangle. As the Pythagorean Theorem only applies to right angle triangles, this would not be the recommended method. You can divide an isoceles triangle into 2 right angle triangles and solve to prove the hypothenuese is the same. Applying the Theorem incorrectly is not the way to teach. This had me questioning other things being taught in this book.