I may have got this wrong because i dont like radian conversions but anyways here goes:
Sin(2x-1) = 1
2x-1 = 90 , 450 , 810
2x = pi/2 + 1, 5pi/2 + 1, 9pi/2 + 1
2x = 3pi/2, 7pi/2, 11pi/2
x = 3pi / 4, 7pi/4, 11pi/4
Therefore a = 3pi/4
and the common difference = pi
Tn= 3pi/4 +...