3~4求公差,解答

2025-01-01 01:30:23
推荐回答(2个)
回答1:


写在纸上请仔细看看

回答2:

a3=a1+2d=6,a6=a1+5d=12,a1=2,d=2,a9=a1+8d=2+8×2=18,Sn=n+2(n-1)/n