Ответ: 2850.
Объяснение:
an=a1+(n-1)d.
a3=a1+2d;
a2=a1+d;
----------------
По условию:
a1+a3= -8;
a1+a1+2d = -8;
2a1+2d= -8;
a1+d = -4;
a1=-4-d;
----------
(a1+d)*(a1+2d)=8;
-4(a1+2d)=8;
a1+2d=-2;
-4-d+2d=-2;
d=2;
a1=-4-2
a1=-6;
------------
Sn=n*(a1+an)/2;
a57=a1+56d=-6+56*2;
a57=106;
S57 = 57(-6+106)/2=57*100/2=2850.
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Answers & Comments
Ответ: 2850.
Объяснение:
an=a1+(n-1)d.
a3=a1+2d;
a2=a1+d;
----------------
По условию:
a1+a3= -8;
a1+a1+2d = -8;
2a1+2d= -8;
a1+d = -4;
a1=-4-d;
----------
(a1+d)*(a1+2d)=8;
-4(a1+2d)=8;
a1+2d=-2;
-4-d+2d=-2;
d=2;
a1=-4-2
a1=-6;
------------
Sn=n*(a1+an)/2;
a57=a1+56d=-6+56*2;
a57=106;
S57 = 57(-6+106)/2=57*100/2=2850.