Harry Kretz taught high school math for many years at Hawthorn Valley Waldorf School in Upstate New York. Since retiring from full-time work, he has worked more than full time traveling and teaching courses in various Waldorf schools and teacher training centers.
Trigonometry: A Practical Introduction presents an approach that involves the whole being of students so they develop clarity of thought and enthusiastic involvement in challenging, meaningful activities. The author advises that, when students work outdoors or are at at their desks measuring distances and angles, the topics being discussed are better understood. Topics include tight triangle calculations; oblique triangle calculations; surveying problems; and much more, with helpful notes and suggestions.