Chứng tỏ: (a - b + c) - (a + c) = -b

Chứng tỏ:
1)(a-b+c)-(a+c)= -b
2)(a+b)-(b-a)+c= 2a+c
3) -(a+b-c)+(a-b-c)= -2b
4) a(b+c)- a(b+d)= a(c-d)
5)a(b-c)+ a(d+c)=a(b+d)