a) \(a.\left(b+c\right)-b.\left(a-c\right)=a.b+a.c-b.a+b.c=a.c+b.c=c.\left(a+b\right)\)
b) \(a.\left(b-c\right)-a.\left(b+d\right)=a.b-a.c-a.b-a.d=-a.c-a.d=-a.\left(c+d\right)\)
ĐPCM
a)Xét VT(vế trái)=a.(b+c)-b.(a-c) b)Xét VT=a(b-c)-a(b+d)
=ab+ac-ba+bc. =ab-ac-ab-ad=c.(a+b)=VP(vế phải). =-ac-ad =-a(c+d)=VP