a, Ta có: a(b+c)-a(b+d)=ab+ac-ab-ad=ac-ad=a(c-d) (đpcm)
b,Ta có: a(b-c)+a(d+c)=ab-ac+ad+ac=ab+ad=a(b+d) (đpcm)
c,Ta có: a(b-c)-a(b+d)=ab-ac-ab-ad=-ac-ad=-a(c+d) (đpcm)
d,Ta có: (a+b)(c+d)-(a+d)(b+c)=ac+ad+bc+bd-ab-ac-bd-dc=ad+bc-ab-dc=a(d-b)-c(d-b)=(d-b)(a-c) (đpcm)
Chúc bạn học tốt nhé! ^^