1.S4 = 4 * a 1+[4 *(4- 1)]d/2 = 4a 1+6d = 1

S8=......= 8a 1+28d=4

Calculate a1=116d =1/8.

Then represent the formula calculation.

2.a 1 a3 = a 1+2d = a 1+4 a4 = a 1+6

(a 1+4)^2=a 1*(a 1+6)

a 1=-8

So a2=-6.