Odpowiedzi

2009-12-07T20:33:32+01:00
Zad1.
a1 = -3
r = 7

an = a1 + (n-1)*r = -3 + (n-1)*7 = -3 +7n -7 = 7n -10
Sn =[ (a1 +an):2*]*n = 690
[ ( -3 + 7n -10) : 2] = 690
( 7n -13 ) :2 = 690 /*2
7n -13 = 1380
7n = 1380 +13
7n = 1393
n = 199

Dla n = 199 suma wynosi 690