1/ (a-b+c)-(a+c)=-b
=a-b+c-a-c=-b
=(a-a)-(c-c)-b=-b
=0+0-b=-b
=-b=-b
⇒Vậy (a-b+c)-(a+c)=-b
2/(a+b)-(b-a)+c=2a+c
=a+b-b+a+c=2a+c
=(a+a)+(b-b)+c=2a+c
=2a+0+c=2a+c
=2a+c=2a+c
⇒Vậy (a+b)-(b-a)+c=2a+c
3/ -(a+b-c)+(a-b-c)=-2b
=-a-b+c+a-b-c=-2b
=(-a+a)+[(-b)+b]+(c-c)=-2b
=0+(-2b)+0=-2b
⇒Vậy -(a+b-c)+(a-b-c)=-2b
4/a(b+c)-a(b+d)=a(c-d)
=ab+ac-ab-ad=a(c-d)
=a(b+c-b-d)=a(c-b)
=a(c-b)=a(c-b)
⇒Vậy a(b+c)-a(b+d)=a(c-d)
5/(b-c) - a.(b+d) = (ab - ac) - (ab+ad)
= ab -ac - ab - ad
= ab - ab +ac+ad = ac+ad
= a(c+d) = ac+ad
⇒Vậy a(b-c) - a(b+d) = a(c+d)
6/ a.(b-c)-a.(b+d)=-a.(c+d)
=ab-ac-ab-ad=a.(c+d)
=-ac-ad=-a.(c+d)
=a.(b-c)-a.(d+b)=-a(c+d)
⇒Vậy a.(b-c)-a.(b+d)=-a.(c+d)
7/ (a+b).(c+d)-(a+d).(b+c)=(a-c)
Vế trái: (a+b).(c+d)-(a+d).(b+c)
=ac+ad+bc+bd-ab-ac-bd-cd
=ad+bc-ab-cd
=a(d+b)-d(a+c)
= ad-da+c
=(a.a)+(d-d).(a+c)
=0+0.(a+c)
=(a+c)=(a+c)
⇒Vậy (a+b).(c+d)-(a+d).(b+c)=(a-c)
