Angle Side Angle

Angle Side Angle triangle construction. Control angles "A" and "B" by using the sliders, and the length of "side c" by dragging the end points. The resulting values for angle "C" and sides "a" and "b" are shown on the left. Notice that if Angle A + Angle B > 180, you don't get a triangle.

For obtuse angles, or for very large values of side c, you may need to right-click and "zoom out" (control-click on a Mac.)

To solve a triangle of this type, first use the "sums to 180" fact to find angle "C." Then use the Law of Sines twice to find sides "a" and "b," using the invariant (side c)/sin(C).

Also notice that leaving the sliders alone and simply adjusting the length of side c produces a family of similar triangles. How can you see this from thinking about the Law of Sines?

Dave Matthews, March 28, 2007, Created with GeoGebra