Odpowiedzi

2009-11-07T21:37:32+01:00
A1 = -3
r = 2
a9 =a1 +8*r =-3 +8*2 = -3 + 16 = 13
S9 ={[a1 + a9]*9}:;2 = ( 10*9):2 = 90:2 = 45
a20 = -3 + 19 *2 = -3 + 38 = 35
S20 ={[a1 + a20]*20}:2 = (32*20):2 = 640:2 = 320
S =S20 -S9 = 320 - 45 = 275
S - suma wyrazów tego ciągu od a10 do a20 włącznie.
1 1 1
2009-11-07T21:47:08+01:00
A1 = -3
r = 2
a9 =a1 +8*r = 13
a20 = a1 + 19*r= -3 + 19 *2 = 35
S_9 =((a1 + a9)*9):2 = 45
S_20 =((a1 + a20)*20):2 = 320
S_szukany =S_20 -S_9 = 275