Page 249 - aljaber

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r = ± 2.25 a = 144 ()
2.25
. 0 a = −144
:( )
2.25

. 5, 5 + d, 5 + 2d, 5 + 3d, 10

5 + d − 5 = 10 − 5 − 3d

4d = 5

d=5
4

.83 71 61

424

. 6 1 + 7 1 + 8 3 = 22 1
424 2

d =1 a1 = 15 :( ) ( )
)
.n − 14 an = n + 14

Sn −14 = (n − 14) 15 + n  = 15n
2
15n + n2 − 210 − 14n = 30n

n2 − 29n − 210 = 0

(n − 35)(n + 6) = 0 n ) n = 35

.(

:( ) (

k2 − 8 −k = k − 5

k 2 − 2k − 3 = 0

(k − 3)(k + 1) = 0

.k1 + k2 = −1 + 3 = 2 .k2 = 3 k1 = −1