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rd

9, 9 + d, 9 + 2d

9, 11 + d, 29 + 2d

. d = 9r − 11 . 9r = 11 + d

. 9r 2 = 29 + 2d = 29 + 2(9r − 11) = 7 + 18r
. 9r2 − 18r − 7 = 0

9r 2 − 18r − 7 = 0 ⇔ (3r + 1)(3r − 7) = 0

⇔ r = −1 r =7
3 3

. 9r2 = 9  − 1 2 = 1 r = −1
3 3

. 9r2 = 9  7 2 = 49 r =7
3 3

.1

(Series) (.)