Page 252 - aljaber

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S8 = 8 (2a1 + 7 × 6)
2
440 = 4(2a1 + 42)

2a1 = 68

a1 = 34

.a3 = 34 + 2 × 6 = 46

−16 :( ) ()

.6

. S 37 = 37  2 × (−16) + 36 × 6  = 37 × 92 = 3404
2

:( ) ()

a + (a + d) + (a + 2d) = −300

( ) 3a + 3d = −300

a + (a + d) + + (a + 8d) = 300

9a + 36d = 300

( ) 3a + 12d = 100

. 6a + 15d .a + (a + d) + + (a + 5d)

. 9d = 400 () ()

6a + 15d = 6a + 6d + 9d ()
= 2(3a + 3d) + 9d
= 2 ×(−300) + 400 = −200

:( )

. ar5 = 2 ⇒ r2 = 5
ar 7 5 2