Question

Find the sum of the first 20 terms of the sequence 2,8,14,20

Answer 1

Answer:

S20=230

Step-by-step explanation:

2,8,14,20

first determine whether it is arithmetic progression or geometric sequence.

• for AP

Common difference (d) = second term - first term

D=T2-T1 D=T3-T2

D=8-2 D=14-8

D=6 D=6

• Also try for GP

COMMON RATIO= T2/T1

r=T2/T1 r=T3/T2

r=8/2 r=14/8

r=4 r=7/4

therefore, we can conclude that this is AP since we have the same common differences in the sequence

Sn=n/2[2a+(n-1)].

where,

a=first term

n=number of terms

S20=20/2[2*2+(20-1)]

S20=10(4+19)

S20=10(23)

S20=230