Question

1+1,5+2+2,5+... An=? d=? S8=?

Answer 1

a1 = 1 
d = a2 - a1 = 1.5 - 1 = 0,5 

an  =a1 + d(n - 1)
a8 = a1 + 7d 
a8 = 1 + 7*0.5 = 3.5 + 1 = 4.5

S8 = (a1  +a8)/2 * 8 = (1 + 4.5)/2 * 8 = 4* 5.5 = 22

Answer 2

A1=1,
d = А2-А1,Sn=((A1+An)n)/2
 d = 1,5-1=0,5
S8= ((1+4,5) 8)/2= 22
An= А1+ (n-1)*d
An = 1 + (n-1)*0,5