等差数列an的前n项和为Sn=2n²+an+b(a,b为常数) (1)求b的值等差数列an的前n项和为Sn=2n²(2倍n的平方)+an+b(a,b为常数) (1)求b的值(2)若Sn+1大于Sn 对n属于正整数恒成立 求a的取值
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![等差数列an的前n项和为Sn=2n²+an+b(a,b为常数) (1)求b的值等差数列an的前n项和为Sn=2n²(2倍n的平方)+an+b(a,b为常数) (1)求b的值(2)若Sn+1大于Sn 对n属于正整数恒成立 求a的取值](/uploads/image/z/3023422-70-2.jpg?t=%E7%AD%89%E5%B7%AE%E6%95%B0%E5%88%97an%E7%9A%84%E5%89%8Dn%E9%A1%B9%E5%92%8C%E4%B8%BASn%3D2n%26%23178%3B%2Ban%2Bb%EF%BC%88a%2Cb%E4%B8%BA%E5%B8%B8%E6%95%B0%EF%BC%89+%EF%BC%881%EF%BC%89%E6%B1%82b%E7%9A%84%E5%80%BC%E7%AD%89%E5%B7%AE%E6%95%B0%E5%88%97an%E7%9A%84%E5%89%8Dn%E9%A1%B9%E5%92%8C%E4%B8%BASn%3D2n%26%23178%3B%EF%BC%882%E5%80%8Dn%E7%9A%84%E5%B9%B3%E6%96%B9%EF%BC%89%2Ban%2Bb%EF%BC%88a%2Cb%E4%B8%BA%E5%B8%B8%E6%95%B0%EF%BC%89+%EF%BC%881%EF%BC%89%E6%B1%82b%E7%9A%84%E5%80%BC%EF%BC%882%EF%BC%89%E8%8B%A5Sn%2B1%E5%A4%A7%E4%BA%8ESn+%E5%AF%B9n%E5%B1%9E%E4%BA%8E%E6%AD%A3%E6%95%B4%E6%95%B0%E6%81%92%E6%88%90%E7%AB%8B+%E6%B1%82a%E7%9A%84%E5%8F%96%E5%80%BC)
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等差数列an的前n项和为Sn=2n²+an+b(a,b为常数) (1)求b的值等差数列an的前n项和为Sn=2n²(2倍n的平方)+an+b(a,b为常数) (1)求b的值(2)若Sn+1大于Sn 对n属于正整数恒成立 求a的取值
等差数列an的前n项和为Sn=2n²+an+b(a,b为常数) (1)求b的值
等差数列an的前n项和为Sn=2n²(2倍n的平方)+an+b(a,b为常数)
(1)求b的值
(2)若Sn+1大于Sn 对n属于正整数恒成立 求a的取值范围
等差数列an的前n项和为Sn=2n²+an+b(a,b为常数) (1)求b的值等差数列an的前n项和为Sn=2n²(2倍n的平方)+an+b(a,b为常数) (1)求b的值(2)若Sn+1大于Sn 对n属于正整数恒成立 求a的取值
an=a1+(n-1)d Sn=(a1+an)n/2=a1n+dn^2/2-dn/2=2n²+an+b
因此 d=4,b=0,
Sn+1-Sn=2(2n+1)+a=4n+2+a>0 恒成立 a>-6
通项公式
a(n)=s(n)-s(n-1)=4n+a-2
a(1)=2+a=s(1)=2+a+b
b=0
s(n+1)-s(n)=4n+a+2>0
a>-(4n+2)>-6