mathexp: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/var/lib/wims/public_html/bin/mathexp - from package: wims

You may install the required package with command apt-get install {package}

Error in other languages:
mathexp: bevel nie gevind nie
mathexp: comandă negăsită
mathexp: comando não encontrado
mathexp: commande introuvable
mathexp: command not found
mathexp: käsku ei ole
mathexp: không tìm thấy lệnh
mathexp: komanda nerasta
mathexp: Kommando nicht gefunden.
mathexp: kommandot finns inte
mathexp: komut yok
mathexp: nie znaleziono polecenia
mathexp: níor aimsíodh an t-ordú
mathexp: no se encontró la orden
mathexp: no s'ha trobat l'ordre
mathexp: opdracht niet gevonden
mathexp: parancs nem található
mathexp: perintah tidak ditemukan
mathexp: príkaz nenájdený
mathexp: příkaz nenalezen
mathexp: команда не найдена
mathexp: командата не е открита
mathexp: 命令找不到
mathexp: コマンドが見つかりません