Official and supplementary resources for checking your work include:
Complete the exercise once, then wait an hour (or a day) and try it again without looking at your previous answers. Compare both attempts. If they differ, you've found a weak spot.
For more detailed pedagogical explanations and answers to the Kursbuch activities, the Tangram aktuell 1 Lehrerhandbuch provides comprehensive keys for both classroom and homework tasks.
Playing Tangram aktuell 1 has several benefits, including: