ACCESS - Trig Intro
In this activity you have two sliders: a purple slider for the angle A and a green slider for side AB. Adjust the sliders one at a time. Note which slider changes the shape and size of the triangle. Then notice which slider changes only the size of the triangle thus forming similar triangles. Notice what happens to the trig ratio result when you move each slider.
Adapted from Trigonometric Ratios by ayoob http://www.geogebratube.org/material/show/id/12100