А1) S = ((2a1 + d(n-1))/2) ×n = 168
A2) d = -3 -(-1.1) = -1.9
a1 = -3
S= ((2a1 + d(n-1))/2) × n = 8265
B1) d = (25-10)/5 = 3
a1 = 10 - 3×4 = -2
S = 115
B2) d = 5 (311-306)
d до последнего отрицательного члена - 63 .
a63 = -311 + 5×62 = -1 , =>
S63 = -9828