1. Arithmetic series a 10=40, a20=60, available tolerance d=2, and its general formula is

An=40+(n- 10)*2=2n+20, so a 1=22.

Furthermore, the summation formula can be obtained as follows.

sn = 22n+n(n- 1)= n * n+2 1n = 352

Get n= 1 1 or n=-32 (cut).

2. from the question A 1 = 1 and D = 2, the sum formula of arithmetic sequence is

Sn=n+n(n- 1)=n*n

So S 10= 100.