Contact us
Choose a category below so we can get back to you as quickly as possible.
假設數列有2k項,d為公差.顯然有 偶數項的和-奇數項的和=k * d =9 sn=111 =(a1+a2k)*2k/2 =(a1+a1+(2k-1)d)* 2k/2 =(2a1+2kd-d)*k =(2+18-d)k =20k-9 =111 所以k=6,d=3/2 囙此通項公式為an=1+3(n-1)/2
We and our partners use cookies and other technologies to analyze traffic and optimize your experience. View more info and control your cookies settings at any time in our Cookies Policy.