Question

The sum of n term of an ap is 3n^2+5n. what's the series?​

Answer 1

Answer:

S = 3n2 + 5n

S1 = a1 = 3 + 5 = 8

S2 = a1 + a2 = 12 + 10 = 22          

⇒ a2 = S2 - S1 = 22 - 8 =  14

S3 = a1 + a2 + a3  = 27 + 15 = 42

⇒a3 = S3 - S2 =  42 - 22 = 20

∴ Given AP is 8,14,20,.....

Thus a = 8 , d = 6          

Given tm = 164.

164 =  [a + (n -1)d]

164 =  [(8) + (m -1)6]

164 = [8 + 6m - 6]

164 = [2 + 6m]

162= 6m

m = 162 / 6.

Step-by-step explanation:

Answer 2

Answer:

Given:

Sn= 3n²+5n

s1= 3+5 =8 = a

s2= 3x4+ 5x2= 12+10= 22

s3= 3x9+ 5x3= 27+15= 42

wkt, an= Sn - Sn-1

a1=8

a2= 22-8= 14

a3= 42-22= 20

from this, a=1; d=6

AP: 8,14,20,....,nth term

hope it helps u...... ^_^