Page 255 - aljaber

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n  2 × 20 + (n − 1)× (−4) = 60
2
n(44 − 4n) = 120

n2 − 11n + 30 = 0

(n − 5)(n − 6) = 0

n2 = 5 n1 = 6 ( )

.n1 + n2 = 6 + 5 = 11
:( )

.16 ( )

.3 ( )

.13 ( )

.1 −1 = −1 .1 −1 = −1 ()
()
22 32 6

.1 ÷1 = 2 1÷1= 1
22
32 3
:( )
n ≥1

a1rn = a1r n+1 + a1r n+2
a1r n

r2 + r −1 = 0

r = −1 ± 1 + 4 = −1 ± 5
22

.r = −1 + 5 r

2 :( )

()