设数列有2k+1项a1+a3+...+a2k+1=168(a1+a(2k+1))(k+1)/2=1682a(k+1)(k+1)/2=168①a2+a4+...+a2k=140(a2+a2k)k/2=1402a(k+1)k/2=140②①/②(k+1)/k=168/140140k+140=168k28k=140k=5所以有2x5+1=11(a1+a(2k+1))(k+1)/2=1682a(k+1)(k+1)/2=168①这个什么意思阿