Question

123

看到直接嚇到不會寫

(B) 80(x-5)×0.1-60x+300
(C) 80(x-5)×0.9=60x-300
(D) 80(x-5)×0.9=60x+300
A B 15. 有一等差數列共13 項,正中央三項和為96,末三項和為51,求首項為何?
(A) 50
9₁ A₂
as a4
au
51
an as an air all 912 913

Answer 1

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Mer

a6+a7+a8 = 3a1+18d = 96
a11+a12+a13 = 3a1+33d = 51
解聯立得a=50

123

解不出 要怎麽算？

Mer

3a1+18d = 96...(1)
3a1+33d = 51...(2)
(2)-(1)得 15d = -45
d = -3代入(1)
3a1 + 18*(-3) = 96
3a1 = 96+54 = 150
a1 = 50

123

喔 謝謝 我真的眼殘算錯 一直看錯數字 累了