Question

if an=3-4n show a1 a2. a3 and solv sn

Answer 1

Hi ,

an = 3 - 4n

a1 = 3 - 4× 1 = -1

a2 = 3 - 4 × 2 = -5

a3 = 3 - 4 × 3 = 3 - 12 = - 9

First time = a = -1

Common difference = a2 - a1

d = -5 - ( - 1 )

d = -5 + 1 = - 4

Sn = n/2 [ 2a + ( n - 1 )d ]

Sn = n/2 [ 2 ( -1 ) + ( n - 1 ) ( - 4 ) ]

= n/2 [ -2 - 4n + 4 ]

= n/2 [ 2 - 4n ]

= n ( 1 - 2n )

I hope this helps you.

:)