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求解～

uil ail
・9x2.
4. 若數列a> 為等比數列,S表其前項和,且S = 6(a+a),則公比,為=
3-7>
+
并且,如
₁₂ = 6 (a₁ + a²₂) = a₁ + a₂ + a₂ + a ₁ = 6 (a₁ + a₂b(a₁ + a₁r²)
=> A₂+04² = 5(9₁+as)
> artar³² = s(a₁ tar²³) RS
ac
(r+1) (F²³1)
(a₁fa₁²³) = 5(a₁ +₁1²) 9₁21-r*)
T-r
8(2)(0) (0)
1-5=
= 2²-1-4x2¹ = -8x2¹ -1
KRS
-+-1=6
-(ar+a)(r+l)
-Q₁ (rl) (71) (1)
(0)
(+K)
r=-1
-1 =7
(A)
-S=-8
S = E
()

Answer 1

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Finnja

S4=a1+a2+a3+a4移項
你應該卡在這
移項相減得a2+a4=5(a1+a3)

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