D=(a5-a1)/4=(9-17)/4=-8/4=-2
S8=(2a1+7d)*8/2=(34-14)*4=20*4=80
640:8-160:(52:13)-(54:9*4+56)=5120*9-(160:4)-(6*4+56)=46080-40-80=45960
1239456*78=96.677.568
5678432*234=1.328.753.088
1.328.753.088:1=1.328.753.088
1.328.753.088-96.677.568=1.232.075.520
Х•(-4)=-36
Х= -36:(-4)
Х= 9