Question

Find sum of 1st 21 term of ap whose 2nd term is 8 and 4th term is 4

Answer 1

Hi, frnd

It is given that 2t is8,4t is 6so 3t= x

8-x=x-4.

X=6

The same way1t=10

10,8,6,4............d=-2

By applying formla

S=n/2*2a+n-1*d

S=21/2*20+-40

S=-210

Hope u got ur ans

Comment

Answer 2

I hope this will help you