.SXM File Extension
What is an SXM file?
Math formula originally created by StarMath but still supported by Apache OpenOffice Math (previously part of OpenOffice.org), the successor to StarMath; saves a mathematical formula using an older file format before Apache OpenOffice adopted the OpenDocument specification.
NOTE: StarMath originally used .SMF files through version 5. However, StarMath 6 and Apache OpenOffice version 1 both use the SXM format. Apache OpenOffice Math formulas now use the .ODF (OpenDocument Formula) extension.