x^2-6x+9;
=x^2-2×x×3+3² 完全平方
=(x-3)²
9(x+y)^2-6(x+y)+1
=[3(x+y)]²-2×3(x+y)×1+1² 完全平方
=[3(x+y)-1]²
=(3x+3y-1)²
x^2-6x+9;9(x+y)^2-6(x+y)+1
x^2-6x+9;
=x^2-2×x×3+3² 完全平方
=(x-3)²
9(x+y)^2-6(x+y)+1
=[3(x+y)]²-2×3(x+y)×1+1² 完全平方
=[3(x+y)-1]²
=(3x+3y-1)²