3x平方+6xy+3y平方=3(x平方+2xy+y平方)=3(x+y)平方
3x的平方+6xy+3y的平方=3(x²+2xy+y²)=3(x+y)²
3x²+6xy+3y²=3(x²+2xy+y²) =3(x+y)²
3x^2+6xy+3y^2=3(x^2+2xy+y^2)=3(x+y)^2
