Oblicz a1, r, an, , a30, S30 w ciągu arytmetycznym. (a1, r, a30 obliczyłam )
Dinka: a3 =8
a10 =29
13 mar 17:18
Tragos: a
3 = 8
a
10 = 29
a
10 − a
3 = 29 − 8
a
1 + 9r − a
1 − 2r = 21
7r = 21
r = 3
a
3 = a
1 + 2r
8 = a
1 + 6
a
1 = 2
a
30 = a
1 + 29r = 2 + 29 * 3 = 89
| | a1 + a30 | |
S30 = |
| * 30 = 15(2 + 89) = 15 * 91 = 1365 |
| | 2 | |
13 mar 17:31