設(shè)等差數(shù)列{an}(n∈正整數(shù))的前n項(xiàng)和為Sn,該數(shù)列是單調(diào)遞增數(shù)列,若S4≥10,S5≤15,則a4的取值范圍

設(shè)等差數(shù)列{an}(n∈正整數(shù))的前n項(xiàng)和為Sn,該數(shù)列是單調(diào)遞增數(shù)列,若S4≥10,S5≤15,則a4的取值范圍
請(qǐng)用待定系數(shù)法來(lái)解決這道題,我不會(huì)求最小值.待定系數(shù)法,待定系數(shù)法,待定系數(shù)法,待定系數(shù)法,待定系數(shù)法,待定系數(shù)法,待定系數(shù)法,不要其他方法.

數(shù)學(xué)人氣：693 ℃時(shí)間：2019-08-18 10:05:57

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