A1=6
d=4-6=-2
a12=a1+11d=6+11*(-2)=-16
S12=((6+(-16))/2)*(-16)=-80
Х*(100+12)/100*(100-24)/100=х-186
х*1,12*0,76=х-186
0,8512х=х-186
х-0,8512х=186
0,1488х=186
х=186/0,1488=1250
3х²+bx+12=0
D=b²-4*3*12=b²-144 < 0
b²-144<0
(b-12)(b+12)<0
+ - +
-------- -12---------- 12 ----------
\\\\\\\\\\\
-12 < b < 12