b2KIT

Law of Sines & Cosines Visualizer

Interactive triangle demonstrating the law of sines and cosines. Drag vertices and watch ratios and formulas update.

Tested tool guide Tested browser tools Checked August 16, 2026

What Law of Sines & Cosines Visualizer does and how it behaves

Move a vertex to reshape the triangle and observe the law of sines and law of cosines update for the new geometry. The visualizer connects each side length with its opposite angle, making it useful for seeing why both laws describe the same triangle from different sets of measurements. The most common mistake is pairing a side with an adjacent angle in the sine ratio. Each side must be paired with the angle directly opposite it.

How the result is produced

1

Vertex-driven measurements

Dragging any vertex changes the three side lengths and usually all three interior angles. The displayed relationships are recalculated from that single drawn triangle. Moving a vertex toward the opposite side produces a flatter triangle, while moving it away changes the balance between the opposite side and angle. The diagram therefore acts as the input rather than merely illustrating a fixed calculation.

2

Linked triangle identities

The sine relationship compares opposite pairs as a/sin(A) = b/sin(B) = c/sin(C). The cosine relationship combines all three sides with one included angle, such as c^2 = a^2 + b^2 - 2ab cos(C). As the shape changes, the numerical terms change while these equalities continue to describe the current nondegenerate triangle.

Good uses

  • Checking whether a handwritten law-of-sines calculation paired each labeled side with the correct opposite angle before continuing with the arithmetic.
  • Exploring how an obtuse angle affects its opposite side and why the longest side lies across from the largest angle in the displayed triangle.
  • Studying the SSA ambiguous case visually by arranging different triangle shapes that may satisfy the same two-side and non-included-angle constraints.

Limits and checks

  • The drawing presents one triangle configuration at a time. In an SSA problem, seeing one valid configuration does not establish that it is the only possible solution.
  • Values shown with limited decimal precision can make ratios or substituted cosine expressions appear slightly unequal when recalculated from the rounded display.
  • A nearly collinear set of vertices represents a nearly degenerate triangle. At exact degeneracy, ordinary interior-triangle interpretation fails and sine ratios can become undefined.

Common questions

Can the visualizer decide whether an SSA problem has two solutions?

Not from one displayed configuration alone. It can help illustrate the ambiguity by showing differently shaped triangles, but the current drawing represents only one triangle at a time. To decide whether zero, one, or two triangles satisfy particular SSA measurements, analyze the given constraints and check every candidate angle and side against them.

Which formula should I watch for my known measurements?

Use the cosine relationship when the known data are three sides or two sides with their included angle. Use the sine relationship when a complete opposite side-angle pair is known along with another side or angle. For SSA data, the sine calculation may produce a supplementary angle that also needs checking against the remaining measurements.

References and verification

The behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.

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