Question

Write an A.P whose first term is 20 and common difference is 8.​

Answer 1

Step-by-step explanation:

For 1st  AP

a=8,d=20

For 2nd AP

a′=−30,d′=8

According to the question, Sn=S2n′

⇒2n[2a+(n−1)d]=22n[2a′+(2n−1)d′]

⇒[2(8)+(n−1)20]=2[2(−30)+(2n−1)8]

⇒2×8+n×20−20=2[−60+16n−8]

⇒20n−4=−136+32n

⇒−32n+20n=−136+4

⇒n=11

Hence, the required value of n is 11.