Answer:
Step-by-step explanation:
15) t = 1 , 3t - 2 = 3*1 - 2 = 3 - 2 = 1
t =2, 3t - 2 = 3*2 - 2 = 6 -2 = 4
t = 3, 3t - 2 = 3*3 - 2 = 9 - 2 = 7
t = 4 , 3t - 2 = 3*4 - 2 = 12 - 2 = 10
Series : 1,4,7,10,.........
a = first term = 1
d = common difference = 2nd term - first term = 4 - 1 = 3
n = number of terms = 20
S = [tex]\frac{n}{2}*(2a + (n-1)d)[/tex]
[tex]=\frac{20}{2}(2*1 +19*3)\\\\= 10 * (2 + 57)\\\\= 10* 59\\\\= 590[/tex]
