Two sides and a non-included angle can give no triangle, one triangle or two triangles. Do not assume that the principal inverse-sine answer is the only possibility.
| Check | Consequence |
|---|---|
| Calculated \(\sin B>1\) | No triangle has this data. |
| Calculated \(\sin B=k\), with \(0<k<1\) | Check both \(B_1=\sin^{-1}(k)\) and \(B_2=180^\circ-B_1\). |
| For each candidate, \(A+B<180^\circ\) | Only candidates leaving a positive third angle are valid. |
If \(\sin B=1\), then \(B=90^\circ\): the supplementary value is the same angle, not a second triangle. It still needs a positive third angle.
Check side-angle ordering as well: a longer side is opposite a larger angle. Report each valid triangle separately, and use unrounded angles for any subsequent side or area calculation.
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