設(shè)等差數(shù)列為{an}
1-(-3)=5-1=4,數(shù)列是以-3為首項(xiàng),4為公差的等差數(shù)列
an=-3+4(n-1)=4n-7
Sn=(a1+an)n/2
=(-3+4n-7)n/2
=2n²-5n
令2n²-5n=150
2n²-5n-150=0
(2n+15)(n-10)=0
n=-15/2(n為正整數(shù),舍去)或n=10
數(shù)列前10項(xiàng)的和是150.