设等差数列(An)的前n项和为Sn,以知A4=14.S10=185,求等差数列(An)的通项An

发布时间:2021-03-07 11:46:53

设等差数列(An)的前n项和为Sn,以知A4=14.S10=185,求等差数列(An)的通项An

网友回答

假设公差为K
由题可知Sn = nA1 +n(n-1)k/2
A4= A1 + 3K = 14
S10= 10A1 + 45K =185
K = 3 ; A1 = 5
An = 5+ 3(n-1) = 3n+2
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