Question

how many terms of the ap 3,7,11....make the sum of 820​

Answer 1

Answer:

hehhdjSolution(By Examveda Team)

The A.P. is 3, 7, 11, 15, ......

Where a = 3, d = 7 - 3 = 4 and sum Sn = 406

∴Sn=n2[2a+(n−1)d]⇒406=n2[2×3×(n−1)×4]⇒812=n(6+4n−4)⇒812=n(4n+2)⇒4n2+2n−812=0⇒2n2+n−406=0⇒2n2+29n−28n−406=0⇒n(2n+29)−14(2n+29)=0⇒(2n+29)(n−14)=0∴n=14or−292Butn=−292isnotpossible

Answer 2

Answer: just solve this quadratic equation

Step-by-step explanation:

2n^2+n - 820