等差数列an中 ,a1=23,公差d为整数,若a6>0,a7

问题描述:

等差数列an中 ,a1=23,公差d为整数,若a6>0,a7

设an=a1+(n-1)d
(1):
a6=a1+5d>0.(1)
a7=a1+6d