For triangle DEF, angle D = 42 degrees, line e = 30 meters and line d = 25 meters. Determine the number of possible triangles that can be constructed. Show work.

  2 triangles

Step-by-step explanation:

The given angle is opposite the shorter of the given sides, so the number of triangles is 2. (30/25·sin(42°) ≈ 0.8 < 1)

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Additional comment

For the case where the shorter given side is opposite the given angle, there is the possibility that the triangle could be a right triangle (1 solution) or that there may be no solutions. You can tell the difference by computing ...

  (long side)/(short side) × sin(given angle)

If this result is exactly 1, the triangle is a right triangle. If it is greater than 1, the triangle cannot exist (no solutions). Since the sines of most angles are irrational, it is unlikely you will see this result be exactly 1 (except for a 30°-60°-90° right triangle).

These observations are a consequence of the Law of Sines, which tells you ...

  sin(A) = (a/b)sin(B)

For real angles, sin(A) ≤ 1.

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