N15
1)x-(2x-(4x+3))=x-(2x-4x-3)=x+2x+3=3x+3
2)8m-(4n-(6m+(3n+5m)))=8m-(4n-(6m+3n+5m))=8m-(4n-6m-3n-5m)=8m-4n+6m+3n+5m=19m-n
N16
3(x-2)-5(4+×)+2(×+13=3×-6-20-5×+2×+26=3×-5×+2×-6-20+26=-2×+2×-26+26=0
2)2a-(a-(1+4a))+4-a-(4a-7)=2a-(a-1-4a)+4-a-4a+7=2a-a+1+4a+4-a-4a+7=2a-a+4a-a-4a+1+4+7=12
N17)
1)a-b+3c=6+3×5=6+15=21
2)c(b-a)=5×6=30
3)4(a-b)/c-3(a-b)=4×6/5-3×6=24/5-18=4,8-18=-13,2
4)3/c-2/a-b=3/5-2/6=3/5-1/3=(9-5)/15=4/15;