METRONMETHOD. REASON. LEARN.
Interactive tool

Triangle and angle explorer

Change two angles to construct a triangle and find the third. The side lengths in the drawing are illustrative.

Your experiment

Change any value to update the result. Use the stated units.

What the numbers tell us

Enable JavaScript to calculate with your own values.

Why it works

A + B + C = 180°

Assumptions and limits

This is a triangle in flat Euclidean geometry. All angles must be positive and their total is 180°.

Try a small challenge

Two angles are 40° and 65°. What is the third?
A little hint

Subtract both from 180.

Understand the idea: Pythagoras’ theorem →