因为数列为等差数列由a4+a5+a6+a7+ +a14=77得11a9=77∴a9=7它又由a4+a7+a10=18得3a7=6②由①②可得首项a1=3,d=1/2由等差数列通项公式an=a1+(n-1)d得ak=a1+(k-1)d=13所以3+1/2（k-1）=13,k=21看看好似不是数字发错了,...a4+a5.....+a14=77(a4+a14)*11/2=77(a+3d)+(a+13d)=14a+8d=7a4+a7+a10=173a7=173(a+6d)=173a+18d=17a+8d=7d=2/3,a=5/35/3+(k-1)*2/3=135+2k-2=39k=18朋友对不起了，因为惯性把a4+a7+a10=17看成了a4+a7+a10=18