Question

Cho A= a+b-5  ;  B = -b - c + 1 ;    C = b-c-4   ; D = b - a 

Chứng minh rằng A + B = C - D

Answer 1

A-B=a+b-5+(-b)-c+1=[b+(-b)]+(a-c)-(5-1)=a-c-4

C-D=b-c-4-b+a=(b-b)+(a-c)-4=a-c-4

suy ra : A+B=C-D