直角三角形計算ツール
The detailed guide below is currently available in English.
Two sides, or one side and one angle
A right triangle has five unknowns worth finding — three sides and two acute angles — and any two independent facts pin it down. Two known sides go through the Pythagorean theorem for the third side, then basic trigonometry for the angles: sin A = a/c and sin B = b/c. A known angle swaps the roles: multiply the hypotenuse by sin of the angle to get the opposite leg, or divide a known leg by tan of its angle to get its neighbor.
Keeping the labels straight
Convention here: legs a and b sit on either side of the right angle, c is the hypotenuse, and angle A faces leg a while angle B faces leg b. Mixing up opposite and adjacent is the classic trig error, so double-check which angle you measured before entering it. Angles must be strictly between 0° and 90° — at the extremes the triangle collapses into a line.
よくある質問
What if I know two angles instead of two sides?
Two angles add no new information: the right angle plus one acute angle already forces the other to be 90° minus it. The shape is fixed but its size is not, so you still need one side — use the Side + Angle tab.
Can the hypotenuse be the shortest side I enter?
No. The hypotenuse always faces the 90° angle and is the longest side. If c entered next to a leg comes out shorter, the values cannot belong to the same right triangle, and the calculator says so.