Question

ʏᴜʏᴜ

請問接下來該怎麼算（我不確定前面寫的對不對）

2.設 > 為等比數列,且滿足 an + ang = 15、anz + as = 30,試求 as。(10分)
解
one piratr
10
9₁r² (1+1²) = 15
|a₁r" (1+r²) = 30
+= = = = 1/2/3 = 11² = 2
07-1=r=2
10
12
ja₁ r¹² + a₁ r¹² = 15
| a₁ r " +9₁ r¹²³ = 30
=>3
15
Q₁ X² (1A23 - 30
r
[2-1]

Answer 1

✨ 最佳解答 ✨

Ny-Ålesund

把 r = 2 代回 (1)
a1 r^10 (1 + 2^2) = 15
=> a1 r^10 = 3 = a11

a16 = a11 r^5 = 3 * 2^5 = 3 * 32 = 96