Question

find the sum of first ten terms of an A.P. having a2=9 amd a4 =13​

Answer 1

Given :

a2 = a + d = 9

a4 = a + 3d = 13

--> a + d = 9............. (I)

--> ±a ±3d = ±13............ (ii)

Change the signs in order to subtract [elimination method....]

Therefore a on both equation I and ll

--> - 2d = - 14

--> d = - 14/-2

--> d = 7...............(iii)

Substituting (iii) in (i)

--> a = 9 - d

--> a = 9 - 7

--> a = 2