Bài 2 :
a,
\(a-\left(b+a\right)=-b\)
b,
\(\left(a+b+c\right)-\left(a+b-c\right)\)
= \(a+b+c-a-b+c\)
= \(2c\)
c,
\(\left(a+b-c\right)+\left(a-b+c\right)-\left(b+c-a\right)-\left(a-b-c\right)\)
= \(a+b-c+a-b+c-b-c-a-a+b-c\)
= \(a+b+\left(-c\right)+a+\left(-b\right)+c+\left(-b\right)+\left(-c\right)+\left(-a\right)+\left(-a\right)+b+\left(-c\right)\)
=\(\left(a+a+\left(-a\right)+\left(-a\right)\right)+\left(b+\left(-b\right)+\left(-b+b\right)\right)+\left(-c+c+\left(-c\right)+-c\right)\)
= 0
Bài 1:
\(-1+3-5+7-...-101+103=2x\)
\(\Leftrightarrow\left(3-1\right)+\left(7-5\right)+...+\left(103-101\right)=2x\)
( Có 26 cặp)
\(\Leftrightarrow2+2+...+2=2x\)
(Có 26 c/s 2)
\(\Leftrightarrow2.26=2x\)
\(\Leftrightarrow x=26\)
Vậy x=26
