15abc-5bc² ＝5bc(3a-c)m（a-5）+2（5-a）=m（a-5）-2（a-5）=(m-2)(a-5)（a-4）（a+1）+3a =a²-3a-4+3a=a²-4=(a+2)(a-2)4+12（x-y）+9（x-y）²=2²+2*3(x-y)+[3（x-y）]²=[2+3(x-y)]&...