x²+2xy+2y²-2y+1=x²+2xy+y²+y²－2y+1=(x²+2xy+y²)+(y²－2y+1)=(x＋y)²+(y－1)²因为(x＋y)²≥0,(y－1)²≥0；所以(x＋y)²+(y－1)²≥0代数式x&...