<span>1)
a1=4; an=63; n=16
Sn = </span>(a1+ an)/2*n = (4+63)/2*16=<span>
536
</span>
2)
a1=-1,3; an=-13,7; n=8
Sn = (a1+ an)/2*n = (-1,3-13,7)/2*8=
<span>
-60
</span>
Х²-25-х+5=0
х²-х-20=0
по теореме виета
х1+х2=1
х1*х2=-20
х1=-5
х2=4
!!!!!!!!!!!!!!!!!!!!!!!!!!