3道运用平方差公式的计算题[ X+( Y+1 ) ]乘[ X-( Y+1) ] [ A-( B-C ) ]乘[ A+( B-C) ](A-2B+3C)乘(A-2B-3C)

第一个 =(x+y+1)*(x-y-1)
=x〃-xy-x+xy-y〃-y+x-y-1
=x〃-y〃-1

[ X+( Y+1 ) ]乘[ X-( Y+1) ] =X^2-(Y+1)^2=X^2-Y^2-2Y-1
[ A-( B-C ) ]乘[ A+( B-C) ] =A^2-B^2+2BC-C^2
(A-2B+3C)乘(A-2B-3C) =(A+2B)^2-9倍C^2