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