a)
1, -2, 3,-4,5......
b) 1/3,1/2, 3/5, 2/3 , 5/7....
a)1,-2,3,-4,5.......2k+1, -2k,.........................
Pn = n(-1)^(n-1), n={1,2,3,4,5,..............}
b) 1/3, 1/2, 3/5, 2/3, 5/7, 3/4, 7/9, 4/5................
Pn = n/(n+2), n={1,2,3,4,5,6,............}