This applet can be used to provide convincing evidence for the Laws of Sines and Cosines and, once the laws are established, to provide practice problems. I like to begin by showing just the measure of an angle and its opposite side and turning on the help to see the ratio of the sine of the angle to the length of the opposite side. Repeating this for the other two angle-side pairs and dragging the vertices around to create new triangles suggests that these three ratios are always equal for a given triangle. Similarly, sliding the dot along the line reveals the expressions and calculations associated with the Law of Cosines. To provide practice problems, turn off the help and choose any three of the six possible pieces of information. Drag a vertex (or two or three) to create a new triangle. Check answers by revealing the remaining angle and side measures.
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