题目

9(a-b)²+12(a²-b²)+4(a+b)²
a³-10a²+25a
x²+2x+1-y²
25（m+n-3）²-9（3m-2n）²

提问时间：2021-01-29

答案

9(a-b)²+12(a²-b²)+4(a+b)²=(3(a-b))+2*3*2(a+b)(a-b)+(2(a+b))²=(3(a-b)+2(a+b))²=(5a-b)²a³-10a²+25a=a(a²-2*5*a+5²)=a(a-5)²x²+2x+1-y²=...