【简答题】数列{ a n }的前 n 项和为 S n =2 a n -2,数列{ b n }是首项为 a 1 ,公差不为零的等差数列,且 b 1 , b 3 , b 11 成等比数列. (1)求数列{ a n }与{ b n }的通项公式; (2)求证: <5.< /div>
【简答题】数列{a n }的前n项和为S n =2a n -2,数列{b n }是首项为a 1 ,公差不为零的等差数列,且b 1 ,b 3 ,b 11 成等比数列. (1)求a 1 ,a 2 ,a 3 的值; (2)求数列{a n }与{b n }的通项公式; (3)求证: b 1 a 1 + b 2 a 2 + b 3 a 3 +…+ b n a n <5.
【单选题】Winter is the______season at most hotels in this seaside town, because very few tourists come to stay.
【单选题】数列{a n }是公差不为零的等差数列,且a 7 , a 10 , a 15 是等比数列{b n }的连续三项,若该等比数列的首项b 1 =3,则b n 等于( )
【单选题】Which of the following types of hotels would likely appeal most to pleasure/leisure travelers?