4+3(n-1)=100
4+3n-3=100
3n+1=100
3n=100-1
n=99/3
n=33
(100+4)*33/2
=104*33/2
=3432/2
=1716
18.求等差級數4+7+10+……+100的和為何? (A) 1568 ..-阿摩線上測驗