Dynamic Geometry can be used to gain efficiency and minimize careless errors in class. Here is another that I wish I had had in class. Imagine how much more I could have focused on the students in class by having presentations dynamic and almost error-free. Imagine students having access to the same dynamic files from home.
Here is an example that shows how the measures of the angles of a triangle can be found if the lengths of the three sides are known. Besides the basic algebra, the student would need to know the Pythagorean Theorem and basic right triangle trig definitions. Taking the last step, to the angle measures themselves, could use a trig table, a calculator, or even Google. (But Google will give angle measure in radians, not degrees, so its use should be guided. If you wish, you can google "calculator", flip it into degree mode, and do the inverse calculation).
This file can be found here.