设{a}是公差为正整数的等差数列,若a1+a2+a3=15,a1*a2*a3=80,求a11+a12+a13

来源：学生作业帮助网 编辑：作业帮 时间：2024/11/27 11:33:35
设{a}是公差为正整数的等差数列,若a1+a2+a3=15,a1*a2*a3=80,求a11+a12+a13
xPJ@l$Y" Ȟ%Q<( JOKKOJڪ (1l&@{e罷;o^QbyAv^߾ߋ_;ї}4ӛf~"nPT'1a(K5_,N N+]ѳ{*LiI]0 ѷ=/bMU'{Wç.uzeV/lSafFmm;UG!0qBJ ˋS+Z ٙ#<* GS |%76ucg:4:v`ٱB^

设{a}是公差为正整数的等差数列,若a1+a2+a3=15,a1*a2*a3=80,求a11+a12+a13
设{a}是公差为正整数的等差数列,若a1+a2+a3=15,a1*a2*a3=80,求a11+a12+a13

设{a}是公差为正整数的等差数列,若a1+a2+a3=15,a1*a2*a3=80,求a11+a12+a13
a1+a3=2a2
=>3a2=15
=>a2=5
a+d=5①
a1*a2*a3=80
a1^2*a2(1+2d)=80
=>a1^2*(1+2d)=16②
联立①②
解得,a1=2,a3=8 d=3
a11+a12+a13
=3a12
=3(a1+11d)
=3*(2+33)
=105

设公差为d a1=a2-d a3=a2+d
a1+a2+a3=15 => a2=5
a1*a2*a3=a2*(a2^2-d^2)=80 => d^2=9 d=3(d>0)
a11+a12+a13=3a12=3a2+30d=105

设a,b是正整数,{an}是首项是a,公差为b的等差数列,{bn}是首项是b,公差为a的等差数列且满足a1 设{a}是公差为正整数的等差数列,若a1+a2+a3=15,a1*a2*a3=80,求a11+a12+a13 设等差数列{an}的首项及公差均是正整数,前n项和为sn,且a1>1,a4>6,s3≤12,则a2013=? 设Sn是等差数列{an}的前n项和,若公差d=-3/23.a1>0,则使Sn取最小值的正整数n的值是 已知数列{An},{Bn}都是公差为1的等差数列,其首项分别为a1,b1,且a1+b1=5(a1,b1属于正整数）.设Cn=A(Bn)(n属于正整数,Bn是A的角标）,则数列{Cn}的前十项和等于? 已知数列{An},{Bn}都是公差为1的等差数列,其首项分别为a1,b1,且a1+b1=5(a1,b1属于正整数）.设Cn=A(Bn)(n属于正整数,Bn是A的角标）,则数列{Cn}的前项和等于? 设{a }是公差为2的等差数列,如果a + +a +a .+a =50,.设{a }是公差为2的等差数列,如果a + +a +a .+a =50,那么a +a +a +…+a 其中那个n怎么求得是33解释下!设{a }是公差为2的等差数列，如果a1 + +a4 +a7 ....+a97 =5 已知数列{An},{Bn}都是公差为1的等差数列,其首项分别为a1,b1,且a1+b1=5(a1,b1属于正整数）.设Cn=A(Bn)(n已知数列{An},{Bn}都是公差为1的等差数列，其首项分别为a1,b1,且a1+b1=5(a1,b1属于正整数）。设Cn=A(B 设等差数列｛an｝的公差为d不为0,a1＝9d,若ak是a1与a2k的等比中项,则k＝ 关于等比数列和等差数列的那些事 a,b是正整数，﹛an﹜是首项为a,公差为b的等差数列，﹛bn﹜是首项为b,公比为a的等比数列，且满足a1 11、设等差数列{an}的公差d≠0,a1=4d,若ak是a1与a6的等比中项,则k的值为 7、设等差数列{an}的公差d≠0,a1=4d,若ak是a1与a6的等比中项,则k的值为 设等差数列{an}公差d≠0 a1=4d,若ak是a1与a2k的等比中项,则k的值为 设等差数列{An}的公差d不为0,A1=9d.若Ak是A1与A2k的等比中项,则k等于几 设等差数列{an}的公差d不为0,a1=9d,若ak是a1与a2k的等比中项,则k=? 设等差数列{an}的公差d不为0,a1=9d.若ak是a1与a2k的等比中项,则k=? 设等差数列an的公差d不为0,a1=9d.若ak是a1与a2k的等比中项,则k等于多少? 设等差数列an的公差d不为0,a1=9d,若ak是a1与a2k的等比中项则k=?