2х2-20х+18=0
х2-10х+9=0
х1=1 х2=9
1/(b^3+b^2) - (1-b)/b^2=1/(b^2(b+1)) - (1-b)/b^2=1/(b^2(b+1)) - (1-b^2)/(b^2(b+1))=(1-1+b^2)/(b^2(b+1))=b^2/(b^2(b+1))=1/(b+1)
7+14+21+28+35+42+49+56+63+70+77+84+91+98+105+112+119=1071
15-12*0.5-12*0.5+7
дальше самостоятельно