Geometry
Testing whether an angle is right
The converse. If measured sides satisfy the relation, the included angle is ninety degrees — the basis of squaring corners.
The Formula
Right angle if and only if a^2 + b^2 = c^2
The converse. If measured sides satisfy the relation, the included angle is ninety degrees — the basis of squaring corners.
| Symbol | Meaning | Unit | Notes |
|---|---|---|---|
| a^2 + b^2 - c^2 | Residual | squared units | Zero means exactly square; larger residuals measure how far out of square. |
What Each Symbol Means
a^2 + b^2 - c^2squared units
Residual
Zero means exactly square; larger residuals measure how far out of square.
See It Worked With Real Numbers
A formula on its own does not tell you which number goes where. The how to use the pythagorean theorem page applies this equation to a concrete case, shows every intermediate step, and names the mistakes that produce a wrong answer even when the algebra is right.
Where This Formula Appears
This equation is the working core of How To Use The Pythagorean Theorem, filed under Math. Every number the guide produces comes from substituting into this one line.