x^2+y^2+2x-6y+21=(x²+2x+1)+(y²-6y+9)+11=(x+1)²+(y-3)²+11∵(x+1)²≥0 (y-3)²≥0∴(x+1)²+(y-3)²+11≥11即代数式x^2+y^2+2x-6y+21的最小值是11.那么，这时x,y的值分别是多少？这时x=-1,y=3.