设等差数列an的前n项和为sn,若1≤a5≤4,2≤a6≤3,则s6的取值范围是
来源:学生作业帮助网 编辑:作业帮 时间:2024/07/09 00:57:10
![设等差数列an的前n项和为sn,若1≤a5≤4,2≤a6≤3,则s6的取值范围是](/uploads/image/z/2780386-34-6.jpg?t=%E8%AE%BE%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%2C%E8%8B%A51%E2%89%A4a5%E2%89%A44%2C2%E2%89%A4a6%E2%89%A43%2C%E5%88%99s6%E7%9A%84%E5%8F%96%E5%80%BC%E8%8C%83%E5%9B%B4%E6%98%AF)
xN@E&&L@=b0&˥&h`"h[tg^&_f~}qݔkzL\SR_OЅR2 -B6죞9WiuNxCEϸGD!
设等差数列an的前n项和为sn,若1≤a5≤4,2≤a6≤3,则s6的取值范围是
设等差数列an的前n项和为sn,若1≤a5≤4,2≤a6≤3,则s6的取值范围是
设等差数列an的前n项和为sn,若1≤a5≤4,2≤a6≤3,则s6的取值范围是
a5=a1+4d,a6=a1+5d,
所以1≤a1+4d≤4,2≤a1+5d≤3,
所以-20≤-5a1-20d≤-5,6≤3a1+15d≤9,
两式相加得,-14≤-2a1-5d≤4,
两边同乘以-1,-4≤2a1+5d≤14.
两边同乘以3,-12≤6a1+15d≤42.
又因为S6=6a1+15d,所以-12≤S6≤42.