`(x-2)^2+//x-2y+4//=(1/2 +1/3 +1/4 +...+1/(2021)).(2020.21212121-20202020-2121)`
`⇔(x-2)^2+//x-2y+4//=(1/2 +1/3 +1/4 +...+1/(2021)).(2020.2121.10001-2020.100012121)`
`⇔(x-2)^2+//x-2y+4//=(1/2 +1/3 +1/4 +...+1/(2021)).0`
`⇔(x-2)^2+//x-2y+4//=0`
`⇒x-2=0 ` và `x-2y+4=0`
`⇒x=2` và `y=(x+4)/2 =(2+4)/2 =3`