Sao ở đa thức C có x vậy, đề cho x hay sao thế?
\(C=x-\left[b-\left(c-a-b\right)\right]=x-\left(b-c+a+b\right)=x-b+c-a-b\)
\(=x-2b+c-a\)
\(D=b+\left[a-\left(c-b-a\right)\right]=b+\left(a-c+b+a\right)=b+a-c+b+a\)
\(=2a+2b-c\)
\(C+D=x-2b+c-a+2a+2b-c\)
\(=x+\left(-a+2a\right)+\left(-2b+2b\right)+\left(c-c\right)\)
\(=x+a\)
\(C-D=\left(x-2b+c-a\right)-\left(2a+2b-c\right)\)
\(=x-2b+c-a-2a-2b+c\)
\(=x+\left(-a-2a\right)+\left(-2b-2b\right)+\left(c+c\right)\)
\(=x-3a-4b+2c\)