Senior one mathematics compulsory five - find the general formula of the sequence! (1) 7,77,777,7777,. Find the general term formula of this sequence~ (2) The known sequence {an} is the arithmetic sequence, A1 = f (x + 1), A2 = 0, A3 = f (x-1), where f (x) = x ^ 2-4x + 2, find the general term formula It's mainly the first question! It doesn't matter if you can't work out the second one~

Senior one mathematics compulsory five - find the general formula of the sequence! (1) 7,77,777,7777,. Find the general term formula of this sequence~ (2) The known sequence {an} is the arithmetic sequence, A1 = f (x + 1), A2 = 0, A3 = f (x-1), where f (x) = x ^ 2-4x + 2, find the general term formula It's mainly the first question! It doesn't matter if you can't work out the second one~

1.an=7*[(10^n-1)+(10^n-2)…… +10^0)]
2.a1+a3=2a2
(x+1)^2-4(x+1)+2+(x-1)^2-4(x-1)+2=0
2x^2+2-8x+4=0
x^2-4x+3=0
x1=1,x2=3
∴an=-2+2n
Or an = 2-2n