余弦定理計算機

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はじめに

Law of Cosines Calculator — Solve a triangle side using the law of cosines. Enter Side a, Side b, Included angle C (degrees) to get an instant, accurate result.

計算式

Law of cosines: c² = a² + b² − 2ab×cos(C), solved for side c given two sides a, b and their included angle C (in degrees).

ステップごとの説明

Enter the Side a.
Enter the Side b.
Enter the Included angle C (degrees).
Click Calculate to see your result instantly.

実例

Example: With Side a = 3, Side b = 4, Included angle C (degrees) = 90, the Law of Cosines Calculator gives Side C: 5.

よくある質問

When should I use law of cosines instead of law of sines?

Law of cosines is ideal when you know two sides and the angle between them (SAS), which law of sines can't directly solve.

Does this reduce to the Pythagorean theorem?

Yes — when C = 90°, cos(C) = 0 and the formula becomes c² = a² + b².

What inputs does the Law of Cosines Calculator need?

You'll need to provide: Side a, Side b, Included angle C (degrees). All fields use sensible defaults, so you can see a working example immediately and then adjust the values to match your own numbers.

How accurate is the Law of Cosines Calculator?

The Law of Cosines Calculator applies the formula exactly as calculated — Law of cosines: c² = a² + b² − 2ab×cos(C), solved for side c given two sides a, b and their included angle C (in degrees). — so results are precise for the inputs you provide. Accuracy depends on entering correct, realistic input values.

Is the Law of Cosines Calculator free to use?

Yes, the Law of Cosines Calculator is completely free, requires no signup, and runs instantly in your browser.