[2] – Geometric Sequence
等比數列

影片內容:
00:05 – concept and general term of geometric sequence 等比數列的概念與通項
04:00 – properties of geometric sequence 等比數列的性質
07:35 – illustrative example 1 例子 1
08:16 – illustrative example 2 例子 2
10:43 – illustrative example 3 例子 3

所屬主題:
[高中數學] – Arithmetic and Geometric Sequences 等差與等比數列

Category: S4-S6 Algebra

8 Comments

  • Avatar
    Rzc
    Reply

    in 14:11, the equation 1000*1.03^n is equals ar^(n-1) ?

  • Avatar
    rzc
    Reply

    你好,我想問 2/3*3^-1 為什麼能寫 2/3(1/3)^n-1 ? 因為我看到3^-n= 1/3^n ,但為什麼指數無-(n-1)? thanks

    • Avatar
      Rzc

      in 3:41, why 2/(3*3^(n-1)) equals (2/3)*(1/3)^(n-1) ? as i know, 3^-a = 1/3^a . sorry, i am noob in math. i don’t understand.

    • Admin
      Admin

      Sorry 咁遲先覆你。我將個步驟寫詳細少少,你睇下明唔明。
      \large \begin{aligned}
      \frac{2}{3^n} &= \frac{2}{3\times 3^{n-1}} \\\\
      &= \frac{2}{3} \times \frac{1}{3^{n-1}} \\\\
      &= \frac{2}{3} \times \frac{1^{n-1}}{3^{n-1}} \ \ \ \because 1^{n-1}=1 \\\\
      &= (\frac{2}{3})(\frac{1}{3})^{n-1}
      \end{aligned}

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