-3a^+2a-1/3
=-3（a²-2a/3+1/9)
=-3(a-1/3)²能解释一下吗-3a^+2a-1/3=-3（a²-2a/3+1/9)………………这一步是提取公因式-3=-3(a-1/3)²…………这一步是因为a²-2a/3+1/9=a²-2a/3+(1/3)²=(a-1/3)²如果还不懂，可在追问。祝学习进步！-3a²+2a-1/3= -1/3(9a²+6a-1)= -1/3(3a-1)²对不对