a) an = 7 + (13-1)4 = 7 + 124 = 7 + 48 = 5Sn = (n/2)(a1 + an) = (13/2)(7 + 55) = 6.5 * 62 = 403
б) an = 2 + (40-1)2 = 2 + 392 = 2 + 78 = 8Sn = (40/2)(2 + 80) = 2082 = 1640
в) an = 56 + (11-1)(-3) = 56 + 10(-3) = 56 - 30 = 2Sn = (11/2)(56 + 26) = 5.5(56 + 26) = 5.5*82 = 451
a) an = 7 + (13-1)4 = 7 + 124 = 7 + 48 = 5
Sn = (n/2)(a1 + an) = (13/2)(7 + 55) = 6.5 * 62 = 403
б) an = 2 + (40-1)2 = 2 + 392 = 2 + 78 = 8
Sn = (40/2)(2 + 80) = 2082 = 1640
в) an = 56 + (11-1)(-3) = 56 + 10(-3) = 56 - 30 = 2
Sn = (11/2)(56 + 26) = 5.5(56 + 26) = 5.5*82 = 451