This theorem concerns the length of a segment [i]p[/i] tangent to circles [i]a[/i] and [i]b[/i], each of which is tangent to both kissing circles [i]b[/i] and [i]d[/i]. It was known to mathematician Ajima Naonobu (1732-1798), whose proof used the [url=https://www.geogebra.org/m/tn4uebgj]Law of Cosines[/url].