Răspuns :
2013:(x-2012)=2013
x-2012 = 2013:2013
x-2012 = 1
x=1+2012
x=2013
verificare
2013:(2013-2012) = 2013
2013:1 = 2013
2013=2013 ADEVARAT
x-2012 = 2013:2013
x-2012 = 1
x=1+2012
x=2013
verificare
2013:(2013-2012) = 2013
2013:1 = 2013
2013=2013 ADEVARAT