zhangyi199891：x²+y²-10x+8y+45=x²-10x+25+y²+8y+16+4=(x-5)²+(y+4)²+4∵(x-5)²≥0,(y+4)²≥0∴(x-5)²+(y+4)²+4≥4>0∴无论x、y取何实数,多项式x²+y²...