TH1: x<2012
=>2019-x+2020-x+2012-x=2-4019x
=>-3x+6051=-4019x+2
=>4016x=-6049
=>x=-6049/4016(nhận)
Th2: 2012<=x<2019
=>x-2012+2019-x+2020-x=2-4019x
=>-x+2027=2-4019x
=>4018x=-2025
=>x=-2025/4018(loại)
TH3: 2019<=x<=2020
=>x-2019+2020-x+x-2012=2-4019x
=>2-4019x=x-2011
=>-4020x=-2013
=>x=2013/4020(loại)
TH4: x>=2020
=>x-2019+x-2020+x-2012=2-4019x
=>3x-6051-2+4019x=0
=>4022x=6053
=>x=6053/4022(loại)