计算 1.(a-2b+3)(-a+2b+3) 2.(a+b-c+3)(a-b-c-3) 3.(2分之1m+n)(m-2n)
问题描述:
计算 1.(a-2b+3)(-a+2b+3) 2.(a+b-c+3)(a-b-c-3) 3.(2分之1m+n)(m-2n)
答
1.(a-2b+3)(-a+2b+3)=[3+(2a-b)][3-(a-2b)]=3²-(2a-b)²=9-4a²+4ab-b²2.(a+b-c+3)(a-b-c-3)=[(a-c)+(b+3)][(a-c)-(b+3)]=(a-c)²-(b+3)²=a²-2ac+c²-b²-6b-93.(2分...