Question

If the sum of first 11 terms of an AP is 121 and that of 17 terms is 289. Find the sum
of first n terms.

pls help me ​

Answer 1

Answer:

Sn=n²

Step-by-step explanation:

S11=121

S17=289

Sn=n/2×2a+(n-1)×d

S11=11/2×2a+10d

a+5d=11  ⇒1  (by simplifing above equation)

and S17=n/2×2a +16d

a+8d=17⇒2

a=1 and d=2 by subracting the two equations 1 and 2

and substuting in formula

Sn=n/2×2a+{n-1}×d

Sn=n²

thank you

Answer 2

your answer hope it will help you