Editing Right angle (section)

== Thales' theorem ==
{{multiple image
| align = right
| image1 = 01-Rechter Winkel mittels Thaleskreis.gif
| width1 = 254 
| alt1 = 
| caption1 = Construction of the perpendicular to the half-line h from the point P (applicable not only at the end point A, M is freely selectable), animation at the end with pause 10 s
| image2 = 01-Rechter Winkel mittels Thaleskreis-II.gif
| width2 = 237
| alt2 = 
| caption2 =  Alternative construction if P outside of the half-line h and the distance A to P' is small (B is freely selectable),<br>animation at the end with pause 10 s
| footer = 
}}
{{main|Thales' theorem}}

Thales' theorem states that an angle inscribed in a [[semicircle]] (with a vertex on the semicircle and its defining rays going through the endpoints of the semicircle) is a right angle.

Two application examples in which the right angle and the Thales' theorem are included (see animations).