1：9-x^2-6x+9y^2
=9+9y^2-x^2-6x
=9(1+y^2)-(x^2+6x)
=9(y^2+1)-x(x+6)
2：x^2+8xy+16y^2+3x+3y+2
=x^2+2*x*4y+(4y)^2+3x+3y+2
=(x+4y)^2+3x+3y+2
=(x+4y)^2+3(x+y)+2