Thu gọn các tổng sau: a, (a – b + c – d) – ( a + b + c + d ) b, (-a + b – c) + (a – b) -(a – b + c) c,-(a – b – c) + (b + c + d) – (-a + b+ d)

a, (a – b + c – d) – ( a + b + c + d )

= a -b+c-d -a -b-c-d

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

= 0    -0     +    0     -0

=0

b, (-a + b – c) + (a – b) -(a – b + c)

= -a +b-c +a-b-a+b-c

=-(a-a)+(b-b)-(c-c)

= -0   + 0    – 0

=0

c,-(a – b – c) + (b + c + d) – (-a + b+ d)

=-a +b +c +b+c+d+a-b-d

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

= -0       + b         +  c.2    +0

= (-0) +0      +b + c,2

=    0 + b + c.2

=b     +c.2

@skymeo gửi bn ạ . Chúc bn hc tốt!!