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證明數列為等差或等比數列技巧
證明數列為等差或等比數列技巧
更新时间:2025-05-05 22:54:27

  1、通常用定義法,等差數列:求證an-an-1為一個定值,則為等差數列。

  2、等比數列:求證an/an-1為一個定值,則為等比數列.依題意,不妨設數列中連續3項為:a,aq,aq^2則:a-aq= aq-aq^2即:aq^2-2aq +a =0或:a*(q-1)^2= 0所以隻有:q=1

  3、或者用中項法,等差數列:求證an+1 + an-1=2an,等比數列:求證an+1 * an-1=an平方

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