S6=(2a1+5d)*6/2=57
2a1+5d=19
5d=19-2a1
d=3,8-0,4a1
a1²+(a1+3,8-0,4a1)²+(a1+7,6-0,8a1)²=93
a1²+(0,6a1+3,8)²+(0,2a1+7,6)²-93=0
a1²+0,36a1²+4,56a1+14,44+0,04a1²+3,04a1+57,76-93=0
1,4a1²+7,6a1-20,8=0
7a1²+38a1-104=0
D=1444+2912=4356
√D=66
a1(1)=(-38-66)/14=-52/7=-7 3/7⇒
d1=19/5-2/5*(-52)7=(133+104)/35=237/35=6 27/35
a1(2)=(-38+66)/14=2⇒d2=3,8-0,4*2=3,8-0,8=3