傻仔再發問,數學問題!

7xy-3+8x+9xy-12xy+7x
=7xy-12xy+9xy-8x+7x-3
=4xy-x-3//

5s^2-4-3s^2+2
=5s^2-3s^2-4+2
=2s^2-2
=2(s^2-1)
=s(s-1)(+1)//

2007-09-03 19:20:39 補充：
5s^2-4-3s^2+2=5s^2-3s^2-4+2=2s^2-2=2(s^2-1)=2(s-1)(+1)//

7xy-3+8x+9xy-12xy+7x
=7xy+9xy-12xy+8x+7x-3
=4xy+15x-3#
5s^2-4-3s^2+2
=2s^2-2
=2(s^2-1)
=2(s+1)(s-1)#

7xy-3+8x+9xy-12xy+7x

=4xy+15x-3

5s2(2次方)-4-3s2(2次方)+2

=2s2(2次方)-2