Question

Chứng minh rằng

a, -(a+b-c)+(a-b-c)=-2b

b, a.(b-c)+a.(d+c)=a.(b+d)

Answer 1

a. \(-\left(a+b-c\right)+\left(a-b-c\right)\)

\(=-a-b+c+a-b-c\)

\(=\left(-a+a\right)+\left(c-c\right)+\left[-b+\left(-b\right)\right]\)

\(=-2b\left(đpcm\right)\)

b. \(a.\left(b-c\right)+a\left(d+c\right)\)

\(=a.\left[\left(b-c\right)+\left(d+c\right)\right]\)

\(=a.\left(b-c+d+c\right)\)

\(=a.\left[\left(b+d\right)+\left(-c+c\right)\right]\)

\(=a.\left(b+d\right)\left(đpcm\right)\)