`3x²+3y²+4xy+2x-2y+2=0`
⇒`9x²+9y²+12xy+6x-6y+2=0`
⇒`(3x)²+2.3x(2y+1)+9y²-6y+2=0`
⇒`(3x+2y+1)²-(2y+1)²+9y²-6y+2=0`
⇒`(3x+2y+1)²-4y²-4y-1+9y²-6y+2=0`
⇒`(3x+2y+1)²+5y²-10y+1=0`
⇒`5(3x+2y+1)²-25y²-2.5y.5-25=0`
⇒`5(3x+2y+1)²-(5y-5)²=0`
Ta có `5(3x+2y+1)²-(5y-5)²≥0`
⇒`3x+2y+1=0 , 5y-5=0`
⇒`x=-1 , y=1`
Thay `x=-1 , y=1` vào M ta đc
`M=1`