9x^2+y^2+2z^2-18x+4z-6y+20=0
<=>(9x^2-18x+9)+(y^2-6y+9)+(2z^2+4z+2)=0
<=>9(x^2-2x+1)+(y-3)^2+2(z^2+2z+1)=0
<=>9(x-1)^2+(y-3)^2+2(z+1)^2=0
<=>x=1;y=3;z=-1
Câu 1: Tìm x,y,z thỏa mãn phương trình sau: 9x2+y2+2z2-18x+4z-6y+20=0
9x^2+y^2+2z^2-18x+4z-6y+20=0
<=>(9x^2-18x+9)+(y^2-6y+9)+(2z^2+4z+2)=0
<=>9(x^2-2x+1)+(y-3)^2+2(z^2+2z+1)=0
<=>9(x-1)^2+(y-3)^2+2(z+1)^2=0
<=>x=1;y=3;z=-1