Question

下列各式的括号内填上适当的项：1.a-b-c+d=a+( )=-b-( )

Answer 1

1.a-b-c+d=a+(-b-c+d )=-b-(-a+c-d )

2.（-a+b+c)(a+b-c)=[b-(a-c )][b+ ( a-c )]

3.(a+b-c-d)(a-b+c-d)=[(a-d)+( b-c )][(a-d)-( b-c )]