\(A=a+\left(42-70+18\right)-\left(42+18-a\right)\)
\(A=a+42-70+18-42-18-a\)
\(A=\left(a-a\right)+\left(42-42\right)+\left(18-18\right)-70\)
\(A=0+0+0-70=-70\)
\(c)\left(x-y+z\right)-\left(x-y-z\right)-\left(2x+y\right)\)
\(=x-y+z-x+y+z-2x-y\)
\(=\left(x-x-2x\right)+\left(-y+y-y\right)+\left(z+z\right)\)
\(=-2x-y+2z\)
\(=y-2z+2x\)
k chắc
\(B=a+30+12-\left(-20\right)+\left(-12\right)-\left(2+a\right)\)
\(=a+30+12+20-12-2-a\)
\(=\left(a-a\right)+\left(30+20\right)+\left(12-12\right)-2\)
\(=0+50+0-2=50-2=48\)
